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 A000594 Ramanujan's tau function (or Ramanujan numbers, or tau numbers). (Formerly M5153 N2237) 196

%I M5153 N2237

%S 1,-24,252,-1472,4830,-6048,-16744,84480,-113643,-115920,534612,

%T -370944,-577738,401856,1217160,987136,-6905934,2727432,10661420,

%U -7109760,-4219488,-12830688,18643272,21288960,-25499225,13865712,-73279080,24647168

%N Ramanujan's tau function (or Ramanujan numbers, or tau numbers).

%C Coefficients of the cusp form of weight 12 for the full modular group.

%C It is conjectured that tau(n) is never zero (this has been verified for n < 816212624008487344127999, see the Derickx, van Hoeij, Zeng reference).

%C M. J. Hopkins mentions that the only known primes p for which tau(p) == 1 (mod p) are 11, 23 and 691, that it is an open problem to decide if there are infinitely many such p and that no others are known below 35000. Simon Plouffe has now searched up to tau(314747) and found no other examples. - _N. J. A. Sloane_, Mar 25 2007

%C Number 1 of the 74 eta-quotients listed in Table I of Martin (1996).

%C With Dedekind's eta function and the discriminant Delta one has eta(z)^24 = Delta(z)/(2*Pi)^12 = Sum_{m >= 1} tau(m)*q^m, with q = exp(2*Pi*i*z), and z in the complex upper half plane, where i is the imaginary unit. Delta is the eigenfunction of the Hecke operator T_n (n >= 1) with eigenvalue tau(n): T_n Delta = tau(n) Delta. From this the formula for tau(m)*tau(n) given below in the formula section follows. See, e.g., the Koecher-Krieg reference, Lemma and Satz, p. 212. Or the Apostol reference, eq. (3) on p. 114 and the first part of section 6.13 on p. 131. - _Wolfdieter Lang_, Jan 26 2016

%C For the functional equation satisfied by the Dirichlet series F(s), Re(s) > 7, of a(n) see the Hardy reference, p. 173, (10.9.4). It is (2*Pi)^(-s) * Gamma(s) * F(s) = (2*Pi)^(s-12) * Gamma(12-s) * F(12-s). This is attributed to J. R. Wilton, 1929, on p. 185. - _Wolfdieter Lang_, Feb 08 2017

%D Tom M. Apostol, Modular functions and Dirichlet series in number theory, second Edition, Springer, 1990, pp. 114, 131.

%D G. Everest, A. van der Poorten, I. Shparlinski and T. Ward, Recurrence Sequences, Amer. Math. Soc., 2003; see esp. p. 255.

%D Farkas and Kra, Theta constants, Riemann surfaces and the modular group, AMS 2001; see p. 298.

%D N. J. Fine, Basic Hypergeometric Series and Applications, Amer. Math. Soc., 1988; p. 77, Eq. (32.2).

%D G. H. Hardy, Ramanujan: twelve lectures on subjects suggested by his life and work, AMS Chelsea Publishing, Providence, Rhode Island, 2002, lecture X, pp. 161-185.

%D M. J. Hopkins, Algebraic topology and modular forms, Proc. Internat. Congress Math., Beijing 2002, Vol. I, pp. 291-317.

%D Bruce Jordan and Blair Kelly (blair.kelly(AT)att.net), The vanishing of the Ramanujan tau function, preprint, 2001.

%D Max Koecher and Aloys Krieg, Elliptische Funktionen und Modulformen, 2. Auflage, Springer, 2007, pp. 210 - 212.

%D N. Laptyeva, V. K. Murty, Fourier coefficients of forms of CM-type, Indian Journal of Pure and Applied Mathematics, October 2014, Volume 45, Issue 5, pp 747-758

%D Yu. I. Manin, Mathematics and Physics, Birkhäuser, Boston, 1981.

%D H. McKean and V. Moll. Elliptic Curves, Camb. Univ. Press, p. 139.

%D M. Ram Murty, The Ramanujan tau-function, pp. 269-288 of G. E. Andrews et al., editors, Ramanujan Revisited. Academic Press, NY, 1988.

%D S. Ramanujan, On Certain Arithmetical Functions. Collected Papers of Srinivasa Ramanujan, p. 153, Ed. G. H. Hardy et al., AMS Chelsea 2000.

%D S. Ramanujan, On Certain Arithmetical Functions. Ramanujan's Papers, p. 196, Ed. B. J. Venkatachala et al., Prism Books, Bangalore 2000.

%D J.-P. Serre, A course in Arithmetic, Springer-Verlag, 1973, see p. 98.

%D J. H. Silverman, Advanced Topics in the Arithmetic of Elliptic Curves, Springer, see p. 482.

%D N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).

%D N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

%D H. P. F. Swinnerton-Dyer, Congruence properties of tau(n), pp. 289-311 of G. E. Andrews et al., editors, Ramanujan Revisited. Academic Press, NY, 1988.

%D Van der Blij, F. "The function tau (n) of S. Ramanujan (an expository lecture)." Math. Student 18 (1950): 83-99.

%D D. Zagier, Introduction to Modular Forms, Chapter 4 in M. Waldschmidt et al., editors, From Number Theory to Physics, Springer-Verlag, 1992.

%D Zagier, Don. "Elliptic modular forms and their applications." The 1-2-3 of modular forms. Springer Berlin Heidelberg, 2008. 1-103.

%H Simon Plouffe, <a href="/A000594/b000594.txt">Table of n, a(n) for n = 1..16090</a>

%H Jennifer S. Balakrishnan, William Craig, and Ken Ono, <a href="https://arxiv.org/abs/2005.10345">Variations of Lehmer's Conjecture for Ramanujan's tau-function</a>, arXiv:2005.10345 [math.NT], 2020.

%H Jennifer S. Balakrishnan, Ken Ono, and Wei-Lun Tsai, <a href="https://arxiv.org/abs/2102.00111">Even values of Ramanujan's tau-function</a>, arXiv:2102.00111 [math.NT], 2021.

%H B. C. Berndt and K. Ono, <a href="http://www.mat.univie.ac.at/~slc/wpapers/s42berndt.pdf">Ramanujan's unpublished manuscript on the partition and tau functions with proofs and commentary</a>

%H B. C. Berndt and K. Ono, <a href="http://emis.dsd.sztaki.hu/journals/SLC/wpapers/s42berndt.html">Ramanujan's unpublished manuscript on the partition and tau functions with proofs and commentary</a>, Séminaire Lotharingien de Combinatoire, B42c (1999), 63 pp.

%H M. Boylan, <a href="http://dx.doi.org/10.1016/S0022-314X(02)00037-9">Exceptional congruences for the coefficients of certain eta-product newforms</a>, J. Number Theory 98 (2003), no. 2, 377-389. MR1955423 (2003k:11071)

%H F. Brunault, <a href="http://www.institut.math.jussieu.fr/~brunault/FonctionTau.pdf">La fonction Tau de Ramanujan</a> {Broken link]

%H D. X. Charles, <a href="http://www.cs.wisc.edu/~cdx/CompTau.pdf">Computing The Ramanujan Tau Function</a>

%H B. Cloitre, <a href="http://bcmathematics.monsite-orange.fr/FractalOrderOfPrimes.pdf ">On the fractal behavior of primes</a>, 2011. [Broken link]

%H Maarten Derickx, Mark van Hoeij, and Jinxiang Zeng, <a href="http://arxiv.org/abs/1312.6819">Computing Galois representations and equations for modular curves X_H(l)</a>, arXiv:1312.6819 [math.NT], (18-March-2014).

%H B. Edixhoven et al., <a href="https://arxiv.org/abs/math/0605244">Computing the coefficients of a modular form</a>, arXiv:math/0605244 [math.NT], 2006-2010.

%H J. A. Ewell, <a href="http://dx.doi.org/10.1090/S0002-9939-99-05289-2">Ramanujan's Tau Function</a>, Proc. Amer. Math. Soc. 128 (2000), 723-726.

%H J. A. Ewell, <a href="http://math.la.asu.edu/~rmmc/rmj/Vol28-2/EWE/EWE.html">Ramanujan's Tau Function</a>

%H Steven R. Finch, <a href="/A000521/a000521_1.pdf">Modular forms on SL_2(Z)</a>, December 28, 2005. [Cached copy, with permission of the author]

%H L. H. Gallardo, <a href="http://www.emis.de/journals/RCM/revistas.art1038.html">On some formulae for Ramanujan's tau function</a>, Rev. Colomb. Matem. 44 (2010) 103-112

%H M. Z. Garaev, V. C. Garcia and S. V. Konyagin, <a href="https://arxiv.org/abs/math/0607169">Waring problem with the Ramanujan tau function</a>, arXiv:math/0607169 [math.NT], 2006.

%H Frank Garvan and Michael J. Schlosser, <a href="https://arxiv.org/abs/1606.08037">Combinatorial interpretations of Ramanujan’s tau function</a>, arXiv:1606.08037 [math.CO], 2016; Discrete Mathematics 341.10 (2018): 2831-2840.

%H H. Gupta, <a href="http://www.currentscience.ac.in/Downloads/article_id_017_06_0179_0180_0.pdf">The Vanishing of Ramanujan's Function(n)</a>, Current Science, 17 (1948), p. 180.

%H J. L. Hafner and J. Stopple, <a href="http://www.wkap.nl/oasis.htm/266553">A Heat Kernel Associated to Ramanujan's Tau Function</a>, The Ramanujan Journal 4(2) 2000.

%H Yang-Hui He and John McKay, <a href="http://arxiv.org/abs/1408.2083">Moonshine and the Meaning of Life</a>, arXiv:1408.2083 [math.NT], 2014.

%H M. Kaneko and D. Zagier, <a href="http://www2.math.kyushu-u.ac.jp/~mkaneko/papers/atkin.pdf">Supersingular j-invariants, hypergeometric series and Atkin's orthogonal polynomials</a>, pp. 97-126 of D. A. Buell and J. T. Teitelbaum, eds., Computational Perspectives on Number Theory, Amer. Math. Soc., 1998

%H Jon Keating and Brady Haran, <a href="https://www.youtube.com/watch?v=VTveQ1ndH1c">The Key to the Riemann Hypothesis</a>, Numberphile video (2016).

%H Martin Klazar, <a href="http://arxiv.org/abs/1808.08449">What is an answer? — remarks, results and problems on PIO formulas in combinatorial enumeration, part I</a>, arXiv:1808.08449 [math.CO], 2018.

%H D. H. Lehmer, <a href="http://dx.doi.org/10.1215/S0012-7094-47-01436-1">The Vanishing of Ramanujan's Function tau(n)</a>, Duke Mathematical Journal, 14 (1947), pp. 429-433.

%H D. H. Lehmer, <a href="/A000594/a000594.pdf">The Vanishing of Ramanujan's Function tau(n)</a>, Duke Mathematical Journal, 14 (1947), pp. 429-433. [Annotated scanned copy]

%H D. H. Lehmer, <a href="http://dx.doi.org/10.1090/S0025-5718-70-99853-4">Tables of Ramanujan's function tau(n)</a>, Math. Comp., 24 (1970), 495-496.

%H LMFDB, <a href="http://www.lmfdb.org/ModularForm/GL2/Q/holomorphic/1/12/1/a/">Newform 1.12.1.a</a>

%H F. Luca and I. E. Shparlinski, <a href="http://www.arXiv.org/abs/math.NT/0607591">Arithmetic properties of the Ramanujan function</a>, arXiv:math/0607591 [math.NT], 2006.

%H N. Lygeros and O. Rozier, <a href="https://cs.uwaterloo.ca/journals/JIS/VOL13/Lygeros/lygeros5.html">A new solution to the equation tau(rho) == 0 (mod p)</a>, J. Int. Seq. 13 (2010) # 10.7.4.

%H Y. Martin, <a href="http://dx.doi.org/10.1090/S0002-9947-96-01743-6">Multiplicative eta-quotients</a>, Trans. Amer. Math. Soc. 348 (1996), no. 12, 4825-4856, see page 4852 Table I.

%H Yuri Matiyasevich, <a href="http://math.colgate.edu/~integers/sjs14/sjs14.Abstract.html">Computational rediscovery of Ramanujan's tau numbers</a>, Integers (2018) 18A, Article #A14.

%H K. Matthews, <a href="http://www.numbertheory.org/php/tau.html">Computing Ramanujan's tau function</a>

%H S. C. Milne, <a href="http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=26345">New infinite families of exact sums of squares formulas, Jacobi elliptic functions and Ramanujan's tau function</a>, Proc. Nat. Acad. Sci. USA, 93 (1996) 15004-15008.

%H S. C. Milne, <a href="http://dx.doi.org/10.1023/A:1014865816981">Infinite families of exact sums of squares formulas, Jacobi elliptic functions, continued fractions and Schur functions</a>, Ramanujan J., 6 (2002), 7-149.

%H Louis J. Mordell, <a href="http://www.archive.org/stream/proceedingsofcam1920191721camb#page/n133">On Mr. Ramanujan's empirical expansions of modular functions</a>, Proceedings of the Cambridge Philosophical Society 19 (1917), pp. 117-124.

%H P. Moree, <a href="http://arXiv.org/abs/math.NT/0201265">On some claims in Ramanujan's 'unpublished' manuscript on the partition and tau functions</a>, arXiv:math/0201265 [math.NT], 2002.

%H M. R. Murty and V. K. Murty, <a href="http://dx.doi.org/10.1007/978-81-322-0770-2_2">The Ramanujan tau-function</a>, in: The mathematical legacy of Srinivasa Ramanujan (Springer, 2012), p 11-23.

%H M. R. Murty, V. K. Murty and T. N. Shorey, <a href="http://archive.numdam.org/article/BSMF_1987__115__391_0.pdf">Odd values of the Ramanujan tau-function</a>, Bulletin de la S. M. F., tome 115 (1987), p. 391-395.

%H Douglas Niebur, <a href="http://projecteuclid.org/euclid.ijm/1256050746">A formula for Ramanujan's tau-function</a>, Illinois Journal of Mathematics, vol.19, no.3, pp.448-449, (1975). - _Joerg Arndt_, Sep 06 2015

%H Oklahoma State Mathematics Department, <a href="http://www.math.okstate.edu/~loriw/degree2/degree2hm/level1/weight12/weight12.html">Ramanujan tau L-Function</a>

%H J. Perry, <a href="http://www.users.globalnet.co.uk/~perry/maths/ramanujantau/ramanujantau.htm">Ramanujan's Tau Function</a> (broken link?)

%H Simon Plouffe, <a href="http://plouffe.fr/OEIS/b000594.txt">The first 225035 terms</a> (432 MB)

%H Simon Plouffe, <a href="http://vixra.org/abs/1409.0048"> Conjectures of the OEIS, as of June 20, 2018.</a>

%H S. Ramanujan, Collected Papers, <a href="http://www.imsc.res.in/~rao/ramanujan/CamUnivCpapers/Cpaper18/page18.htm">Table of tau(n);n=1 to 30</a>

%H J. P. Serre, <a href="http://www.numdam.org/item/SDPP_1967-1968__9_1_A13_0/">An interpretation of some congruences concerning Ramanujan's tau function</a>

%H J. P. Serre, <a href="https://www.researchgate.net/publication/2396158_An_Interpretation_of_some_congruences_concerning_Ramanujan&#39;s_tau-function">An interpretation of some congruences concerning Ramanujan's Tau function</a>

%H J.-P. Serre, <a href="https://doi.org/10.1017/S0017089500006194">Sur la lacunarité des puissances de eta</a>, Glasgow Math. Journal, 27 (1985), 203-221.

%H N. J. A. Sloane, <a href="http://neilsloane.com/doc/sg.txt">My favorite integer sequences</a>, in Sequences and their Applications (Proceedings of SETA '98).

%H N. J. A. Sloane, <a href="https://arxiv.org/abs/math/0207175">My Favorite Integer Sequences</a>, arXiv:math/0207175 [math.CO], 2002.

%H Michael Somos, <a href="/A030203/a030203.txt">Index to Yves Martin's list of 74 multiplicative eta-quotients and their A-numbers</a>

%H D. A. Steffen, <a href="http://www.maths.mq.edu.au/~steffen/old/ramanujan/ramanujan.pdf">Les Coefficients de Fourier de la forme modulaire: La fonction de Ramanujan tau(n)</a>

%H William Stein, <a href="http://wstein.org/">Database</a>

%H H. P. F. Swinnerton-Dyer, <a href="http://dx.doi.org/10.1007/978-3-540-37802-0_1">On l-adic representations and congruences for coefficients of modular forms</a>, pp. 1-55 of Modular Functions of One Variable III (Antwerp 1972), Lect. Notes Math., 350, 1973.

%H G. N. Watson, <a href="http://dx.doi.org/10.1112/plms/s2-51.1.1">A table of Ramanujan's function tau(n)</a>, Proc. London Math. Soc., 51 (1950), 1-13.

%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/TauFunction.html">Tau Function</a>

%H K. S. Williams, <a href="http://people.math.carleton.ca/~williams/papers/pdf/355.pdf">Historical remark on Ramanujan's tau function</a>, Amer. Math. Monthly, 122 (2015), <a href="http://dx.doi.org/10.4169/amer.math.monthly.122.01.30">30-35</a>.

%H <a href="/index/Cor#core">Index entries for "core" sequences</a>

%H <a href="/index/Pro#1mxtok">Index entries for expansions of Product_{k >= 1} (1-x^k)^m</a>

%H <a href="/index/Ch#Cheby">Index entries for sequences related to Chebyshev polynomials.</a>

%F G.f.: x * Product_{k>=1} (1 - x^k)^24 = x*A(x)^8, with the g.f. of A010816.

%F G.f. is a period 1 Fourier series which satisfies f(-1 / t) = (t/i)^12 f(t) where q = exp(2 Pi i t). - _Michael Somos_, Jul 04 2011

%F abs(a(n)) = O(n^(11/2 + epsilon)), abs(a(p)) <= 2 p^(11/2) if p is prime. These were conjectured by Ramanujan and proved by Deligne.

%F Zagier says: The proof of these formulas, if written out from scratch, has been estimated at 2000 pages; in his book Manin cites this as a probable record for the ratio: "length of proof:length of statement" in the whole of mathematics.

%F G.f. A(x) satisfies 0 = f(A(x), A(x^2), A(x^4)) where f(u, v, w) = u*w * (u + 48*v + 4096*w) - v^3. - _Michael Somos_, Jul 19 2004

%F G.f. A(q) satisfies q * d log(A(q))/dq = A006352(q). - _Michael Somos_, Dec 09 2013

%F a(2*n) = A099060(n). a(2*n + 1) = A099059(n). - _Michael Somos_, Apr 17 2015

%F a(n) = tau(n) (with tau(0) = 0): tau(m)*tau(n) = Sum_{d| gcd(m,n)} d^11*tau(m*n/d^2), for positive integers m and n. If gcd(m,n) = 1 this gives the multiplicativity of tau. See a comment above with the Koecher-Krieg reference, p. 212, eq. (5). - _Wolfdieter Lang_, Jan 21 2016

%F Dirichlet series as product: Sum_{n >= 1} a(n)/n^s = Prod_{n >= 1} 1/(1 - a(prime(n))/prime(n)^s + prime(n)^(11-2*s)). See the Mordell link, eq. (2). - _Wolfdieter Lang_, May 06 2016. See also Hardy, p. 164, eqs. (10.3.1) and (10.3.8). - _Wolfdieter Lang_, Jan 27 2017

%F a(n) is multiplicative with a(prime(n)^k) = sqrt(prime(n)^(11))^k*S(k, a(n) / sqrt(prime(n)^(11))), with the Chebyshev S polynomials (A049310), for n >= 1 and k >= 2, and A076847(n) = a(prime(n))). See A076847 for alpha multiplicativity and examples. - _Wolfdieter Lang_, May 17 2016. See also Hardy, p. 164, eq. (10.3.6) rewritten in terms of S. - _Wolfdieter Lang_, Jan 27 2017

%F G.f. eta(z)^24 (with q = exp(2*Pi*i*z)) also (E_4(q)^3 - E_6(q)^2) / 1728. See the Hardy reference, p. 166, eq. (10.5.3), with Q = E_4 and R = E_6, given in A004009 and A013973, respectively. - _Wolfdieter Lang_, Jan 30 2017

%F a(n) (mod 5) == A126832(n).

%F a(1) = 1, a(n) = -(24/(n-1))*Sum_{k=1..n-1} A000203(k)*a(n-k) for n > 1. - _Seiichi Manyama_, Mar 26 2017

%F G.f.: x*exp(-24*Sum_{k>=1} x^k/(k*(1 - x^k))). - _Ilya Gutkovskiy_, Feb 05 2018

%F Euler Transform of [-24, -24, -24, -24, ...]. - _Simon Plouffe_, Jun 21 2018

%e G.f. = q - 24*q^2 + 252*q^3 - 1472*q^4 + 4830*q^5 - 6048*q^6 - 16744*q^7 + 84480*q^8 - 113643*q^9 + ...

%e 35328 = (-24)*(-1472) = a(2)*a(4) = a(2*4) + 2^11*a(2*4/4) = 84480 + 2048*(-24) = 35328. See a comment on T_n Delta = tau(n) Delta above. - _Wolfdieter Lang_, Jan 21 2016

%p M := 50; t1 := series(x*mul((1-x^k)^24,k=1..M),x,M); A000594 := n-> coeff(t1,x,n);

%t CoefficientList[ Take[ Expand[ Product[ (1 - x^k)^24, {k, 1, 30} ]], 30], x] (* Or *)

%t (* first do *) Needs["NumberTheory`Ramanujan`"] (* then *) Table[ RamanujanTau[n], {n, 30}] (* _Dean Hickerson_, Jan 03 2003 *)

%t max = 28; g[k_] := -BernoulliB[k]/(2k) + Sum[ DivisorSigma[k - 1, n - 1]*q^(n - 1), {n, 2, max + 1}]; CoefficientList[ Series[ 8000*g[4]^3 - 147*g[6]^2, {q, 0, max}], q] // Rest (* _Jean-François Alcover_, Oct 10 2012, from modular forms *)

%t RamanujanTau[Range[40]] (* The function RamanujanTau is now part of Mathematica's core language so there is no longer any need to load NumberTheory`Ramanujan` before using it *) (* _Harvey P. Dale_, Oct 12 2012 *)

%t a[ n_] := SeriesCoefficient[ q QPochhammer[ q]^24, {q, 0, n}]; (* _Michael Somos_, May 27 2014 *)

%t a[ n_] := With[{t = Log[q] / (2 Pi I)}, SeriesCoefficient[ Series[ DedekindEta[t]^24, {q, 0, n}], {q, 0, n}]]; (* _Michael Somos_, May 27 2014 *)

%o (Julia)

%o using Nemo

%o function DedekindEta(len, r)

%o R, z = PolynomialRing(ZZ, "z")

%o e = eta_qexp(r, len, z)

%o [coeff(e, j) for j in 0:len - 1] end

%o RamanujanTauList(len) = DedekindEta(len, 24)

%o RamanujanTauList(28) |> println # _Peter Luschny_, Mar 09 2018

%o (MAGMA) M12:=ModularForms(Gamma0(1),12); t1:=Basis(M12)[2]; PowerSeries(t1[1],100); Coefficients(\$1);

%o (MAGMA) Basis( CuspForms( Gamma1(1), 12), 100)[1]; /* _Michael Somos_, May 27 2014 */

%o (PARI) {a(n) = if( n<1, 0, polcoeff( x * eta(x + x * O(x^n))^24, n))};

%o (PARI) {a(n) = if( n<1, 0, polcoeff( x * (sum( i=1, (sqrtint( 8*n - 7) + 1) \ 2,(-1)^i * (2*i - 1) * x^((i^2 - i)/2), O(x^n)))^8, n))};

%o (PARI) taup(p,e)={

%o if(e==1,

%o (65*sigma(p,11)+691*sigma(p,5)-691*252*sum(k=1,p-1,sigma(k,5)*sigma(p-k,5)))/756

%o ,

%o my(t=taup(p,1));

%o sum(j=0,e\2,

%o (-1)^j*binomial(e-j,e-2*j)*p^(11*j)*t^(e-2*j)

%o )

%o )

%o };

%o a(n)=my(f=factor(n));prod(i=1,#f[,1],taup(f[i,1],f[i,2]));

%o \\ _Charles R Greathouse IV_, Apr 22 2013

%o (PARI) \\ compute terms individually (Douglas Niebur, Ill. J. Math., 19, 1975):

%o a(n) = n^4*sigma(n) - 24*sum(k=1, n-1, (35*k^4-52*k^3*n+18*k^2*n^2)*sigma(k)*sigma(n-k));

%o vector(33, n, a(n)) \\ _Joerg Arndt_, Sep 06 2015

%o (PARI) a(n)=ramanujantau(n) \\ _Charles R Greathouse IV_, May 27 2016

%o (Sage) CuspForms( Gamma1(1), 12, prec=100).0; # _Michael Somos_, May 28 2013

%o (Sage) list(delta_qexp(100))[1:] # faster _Peter Luschny_, May 16 2016

%o (Ruby)

%o def s(n)

%o s = 0

%o (1..n).each{|i| s += i if n % i == 0}

%o s

%o end

%o def A000594(n)

%o ary = [1]

%o a = [0] + (1..n - 1).map{|i| s(i)}

%o (1..n - 1).each{|i| ary << (1..i).inject(0){|s, j| s - 24 * a[j] * ary[-j]} / i}

%o ary

%o end

%o p A000594(100) # _Seiichi Manyama_, Mar 26 2017

%o (Ruby)

%o def A000594(n)

%o ary = [0, 1]

%o (2..n).each{|i|

%o s, t, u = 0, 1, 0

%o (1..n).each{|j|

%o t += 9 * j

%o u += j

%o break if i <= u

%o s += (-1) ** (j % 2 + 1) * (2 * j + 1) * (i - t) * ary[-u]

%o }

%o ary << s / (i - 1)

%o }

%o ary[1..-1]

%o end

%o p A000594(100) # _Seiichi Manyama_, Nov 25 2017

%Y Cf. A076847 (tau(prime)), A278577 (prime powers), A037955, A027364, A037945, A037946, A037947, A008408 (Leech).

%Y For a(n) mod N for various values of N see A046694, A098108, A126812-...

%Y Cf. A006352, A099059, A099060, A262339, A292781.

%Y For primes p such that tau(p) == -1 (mod 23) see A106867.

%Y Cf. A010816, A004009. A013973.

%Y Cf. A126832(n) = a(n) mod 5.

%K sign,easy,core,mult,nice

%O 1,2

%A _N. J. A. Sloane_

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Last modified April 21 23:52 EDT 2021. Contains 343156 sequences. (Running on oeis4.)