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A000172 Franel number a(n) = Sum_{k = 0..n} binomial(n,k)^3.
(Formerly M1971 N0781)
112

%I M1971 N0781

%S 1,2,10,56,346,2252,15184,104960,739162,5280932,38165260,278415920,

%T 2046924400,15148345760,112738423360,843126957056,6332299624282,

%U 47737325577620,361077477684436,2739270870994736,20836827035351596

%N Franel number a(n) = Sum_{k = 0..n} binomial(n,k)^3.

%C Cusick gives a general method of deriving recurrences for the r-th order Franel numbers (this is the sequence of third-order Franel numbers), with floor((r+3)/2) terms.

%C This is the Taylor expansion of a special point on a curve described by Beauville. - _Matthijs Coster_, Apr 28 2004

%C a(1) = 2 is the only prime Franel number. Semiprime Franel numbers include: a(2) = 10 = 2 * 5, a(4) = 346 = 2 * 173, a(8) = 739162 = 2 * 369581. - _Jonathan Vos Post_, May 22 2005

%C An identity of V. Strehl states that a(n) = Sum_{k = 0..n} C(n,k)^2 * binomial(2*k,n). Zhi-Wei Sun conjectured that for every n = 2,3,... the polynomial f_n(x) = Sum_{k = 0..n} binomial(n,k)^2 * binomial(2*k,n) * x^(n-k) is irreducible over the field of rational numbers. - _Zhi-Wei Sun_, Mar 21 2013

%C Conjecture: a(n) == 2 (mod n^3) iff n is prime. - _Gary Detlefs_, Mar 22 2013

%C It is trivial that a(p) == 2 (mod p^3) for any prime p since p | C(p,k) for all k = 1,...,p-1. - _Zhi-Wei Sun_, Aug 14 2013

%C a(n) is the maximal number of totally mixed Nash equilibria in games of 3 players, each with n+1 pure options. - _Raimundas Vidunas_, Jan 22 2014

%C This is one of the Apéry-like sequences - see Cross-references. - _Hugo Pfoertner_, Aug 06 2017

%C Diagonal of rational functions 1/(1 - x*y - y*z - x*z - 2*x*y*z), 1/(1 - x - y - z + 4*x*y*z), 1/(1 + y + z + x*y + y*z + x*z + 2*x*y*z), 1/(1 + x + y + z + 2*(x*y + y*z + x*z) + 4*x*y*z). - _Gheorghe Coserea_, Jul 04 2018

%C a(n) is the constant term in the expansion of ((1 + x) * (1 + y) + (1 + 1/x) * (1 + 1/y))^n. - _Seiichi Manyama_, Oct 27 2019

%D Matthijs Coster, Over 6 families van krommen [On 6 families of curves], Master's Thesis (unpublished), Aug 26 1983.

%D J. Franel, Intermédiaire des Mathématiciens, 1894.

%D M. Klamkin, ed., Problems in Applied Mathematics: Selections from SIAM Review, SIAM, 1990; see pp. 148-149.

%D J. Riordan, An Introduction to Combinatorial Analysis, Wiley, 1958, p. 193.

%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).

%H Indranil Ghosh, <a href="/A000172/b000172.txt">Table of n, a(n) for n = 0..1000</a> (terms 0..100 from T. D. Noe)

%H B. Adamczewski, J. P. Bell, E. Delaygue, <a href="http://arxiv.org/abs/1603.04187">Algebraic independence of G-functions and congruences à la Lucas"</a>, arXiv preprint arXiv:1603.04187 [math.NT], 2016.

%H R. Askey, <a href="http://dx.doi.org/10.1137/1.9781611970470">Orthogonal Polynomials and Special Functions</a>, SIAM, 1975; see p. 43.

%H P. Barrucand, <a href="http://dx.doi.org/10.1137/1017013">A combinatorial identity, Problem 75-4</a>, SIAM Rev., 17 (1975), 168. <a href="http://dx.doi.org/10.1137/1018056">Solution</a> by D. R. Breach, D. McCarthy, D. Monk and P. E. O'Neil, SIAM Rev. 18 (1976), 303.

%H P. Barrucand, <a href="/A002893/a002893.pdf">Problem 75-4, A Combinatorial Identity</a>, SIAM Rev., 17 (1975), 168. [Annotated scanned copy of statement of problem]

%H Arnaud Beauville, <a href="http://gallica.bnf.fr/ark:/12148/bpt6k5543443c/f31.item">Les familles stables de courbes sur P_1 admettant quatre fibres singulières</a>, Comptes Rendus, Académie Sciences Paris, no. 294, May 24 1982.

%H David Callan, <a href="http://arxiv.org/abs/0712.3946">A combinatorial interpretation for the identity Sum_{k=0}^{n} binom{n}{k} Sum_{j=0}^{k} binom{k}{j}^{3}= Sum_{k=0}^{n} binom{n}{k}^{2}binom{2k}{k} </a>, arXiv:0712.3946 [math.CO], 2007.

%H D. Callan, <a href="https://cs.uwaterloo.ca/journals/JIS/VOL11/Callan2/callan204.html">A combinatorial interpretation for an identity of Barrucand</a>, JIS 11 (2008) 08.3.4

%H M. Coster, <a href="/A001850/a001850_1.pdf">Email, Nov 1990</a>

%H T. W. Cusick, <a href="http://dx.doi.org/10.1016/0097-3165(89)90063-0">Recurrences for sums of powers of binomial coefficients</a>, J. Combin. Theory, A 52 (1989), 77-83.

%H E. Delaygue, <a href="http://arxiv.org/abs/1310.4131">Arithmetic properties of Apéry-like numbers</a>, arXiv preprint arXiv:1310.4131 [math.NT], 2013.

%H Tomislav Došlic, Darko Veljan, <a href="http://dx.doi.org/10.1016/j.disc.2007.04.066">Logarithmic behavior of some combinatorial sequences</a>, Discrete Math. 308 (2008), no. 11, 2182--2212. MR2404544 (2009j:05019) - From _N. J. A. Sloane_, May 01 2012

%H C. Elsner, <a href="http://www.fq.math.ca/Papers1/43-1/paper43-1-5.pdf">On recurrence formulas for sums involving binomial coefficients</a>, Fib. Q., 43,1 (2005), 31-45.

%H Jeff D. Farmer, Steven C. Leth, <a href="http://www.jstor.org/stable/3621929">An asymptotic formula for powers of binomial coefficients</a>, Math. Gaz. 89 (516) (2005) 385-391.

%H Darij Grinberg, <a href="http://www.cip.ifi.lmu.de/~grinberg/t/19s/notes.pdf">Introduction to Modern Algebra</a> (UMN Spring 2019 Math 4281 Notes), University of Minnesota (2019).

%H Nick Hobson, <a href="/A000172/a000172.py.txt">Python program for this sequence</a>

%H V. Kotesovec, <a href="https://oeis.org/wiki/User:Vaclav_Kotesovec">Non-attacking chess pieces</a>, 6ed, 2013, p. 282.

%H Amita Malik and Armin Straub, <a href="https://doi.org/10.1007/s40993-016-0036-8">Divisibility properties of sporadic Apéry-like numbers</a>, Research in Number Theory, 2016, 2:5

%H R. Mestrovic, <a href="http://arxiv.org/abs/1409.3820">Lucas' theorem: its generalizations, extensions and applications (1878--2014)</a>, arXiv preprint arXiv:1409.3820 [math.NT], 2014.

%H V. Strehl, <a href="http://www.mat.univie.ac.at/~slc/opapers/s29strehl.html">Recurrences and Legendre transform</a>, Séminaire Lotharingien de Combinatoire, B29b (1992), 22 pp.

%H Zhi-Hong Sun, <a href="https://arxiv.org/abs/1803.10051">Congruences for Apéry-like numbers</a>, arXiv:1803.10051 [math.NT], 2018.

%H Z.-W. Sun, <a href="http://arxiv.org/abs/1112.1034">Congruences for Franel numbers</a>, arXiv preprint arXiv:1112.1034 [math.NT], 2011.

%H Zhi-Wei Sun, <a href="http://math.nju.edu.cn/~zwsun/150f.pdf">Connections between p = x^2+3y^2 and Franel numbers</a>, J. Number Theory 133(2013), 2919-2928.

%H Z.-W. Sun, <a href="http://arxiv.org/abs/1208.2683">Conjectures involving arithmetical sequences</a>, arXiv:1208.2683v9 [math.CO] 2013; Number Theory: Arithmetic in Shangri-La (eds., S. Kanemitsu, H. Li and J. Liu), Proc. the 6th China-Japan Sem. (Shanghai, August 15-17, 2011), World Sci., Singapore, 2013, pp. 244-258;

%H Z.-W. Sun, <a href="http://arxiv.org/abs/1407.0967">Congruences involving g_n(x) = Sum_{k= 0..n} C(n,k)^2 C(2k,k) x^k</a>, arXiv preprint arXiv:1407.0967 [math.NT], 2014.

%H R. Vidunas, <a href="http://arxiv.org/abs/1401.5400">MacMahon's master theorem and totally mixed Nash equilibria</a>, arxiv 1401.5400 [math.CO], 2014.

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

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

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

%H D. Zagier, <a href="http://people.mpim-bonn.mpg.de/zagier/files/tex/AperylikeRecEqs/fulltext.pdf">Integral solutions of Apéry-like recurrence equations</a>. See line A in sporadic solutions table of page 5.

%H Bao-Xuan Zhu, <a href="http://arxiv.org/abs/1309.6025">Higher order log-monotonicity of combinatorial sequences</a>, arXiv preprint arXiv:1309.6025 [math.CO], 2013.

%F A002893(n) = Sum_{m = 0..n} binomial(n, m)*a(m) [Barrucand].

%F Sum_{k = 0..n} C(n, k)^3 = (-1)^n*Integral_{x = 0..infinity} L_k(x)^3 exp(-x) dx. - from Askey's book, p. 43

%F (n + 1)^2*a(n+1) = (7*n^2 + 7*n + 2)*a(n) + 8*n^2*a(n-1) [Franel]. - Felix Goldberg (felixg(AT)tx.technion.ac.il), Jan 31 2001

%F a(n) ~ 2*3^(-1/2)*Pi^-1*n^-1*2^(3*n). - Joe Keane (jgk(AT)jgk.org), Jun 21 2002

%F O.g.f.: A(x) = Sum_{n >= 0} (3*n)!/n!^3 * x^(2*n)/(1 - 2*x)^(3*n+1). - _Paul D. Hanna_, Oct 30 2010

%F G.f.: hypergeom([1/3, 2/3], [1], 27 x^2 / (1 - 2x)^3) / (1 - 2x). - _Michael Somos_, Dec 17 2010

%F G.f.: Sum_{n >= 0} a(n)*x^n/n!^3 = [ Sum_{n >= 0} x^n/n!^3 ]^2. - _Paul D. Hanna_, Jan 19 2011

%F G.f.: A(x) = 1/(1-2*x)*(1+6*(x^2)/(G(0)-6*x^2)),

%F with G(k) = 3*(x^2)*(3*k+1)*(3*k+2) + ((1-2*x)^3)*((k+1)^2) - 3*(x^2)*((1-2*x)^3)*((k+1)^2)*(3*k+4)*(3*k+5)/G(k+1) ; (continued fraction). - _Sergei N. Gladkovskii_, Dec 03 2011

%F In 2011 _Zhi-Wei Sun_ found the formula Sum_{k = 0..n} C(2*k,n)*C(2*k,k)* C(2*(n-k),n-k) = 2^n*a(n) and proved it via the Zeilberger algorithm. - _Zhi-Wei Sun_, Mar 20 2013

%F 0 = a(n)*(a(n+1)*(-2048*a(n+2) - 3392*a(n+3) + 768*a(n+4)) + a(n+2)*(-1280*a(n+2) - 2912*a(n+3) + 744*a(n+4)) + a(n+3)*(+288*a(n+3) - 96*a(n+4))) + a(n+1)*(a(n+1)*(-704*a(n+2) - 1232*a(n+3) + 288*a(n+4)) + a(n+2)*(-560*a(n+2) - 1372*a(n+3) + 364*a(n+4)) + a(n+3)*(+154*a(n+3) - 53*a(n+4))) + a(n+2)*(a(n+2)*(+24*a(n+2) + 70*a(n+3) - 20*a(n+4)) + a(n+3)*(-11*a(n+3) + 4*a(n+4))) for all n in Z. - _Michael Somos_, Jul 16 2014

%F For r a nonnegative integer, Sum_{k = r..n} C(k,r)^3*C(n,k)^3 = C(n,r)^3*a(n-r), where we take a(n) = 0 for n < 0. - _Peter Bala_, Jul 27 2016

%F a(n) = (n!)^3 * [x^n] hypergeom([], [1, 1], x)^2. - _Peter Luschny_, May 31 2017

%F From _Gheorghe Coserea_, Jul 04 2018: (Start)

%F a(n) = Sum_{k=0..floor(n/2)} (n+k)!/(k!^3*(n-2*k)!) * 2^(n-2*k).

%F G.f. y=A(x) satisfies: 0 = x*(x + 1)*(8*x - 1)*y'' + (24*x^2 + 14*x - 1)*y' + 2*(4*x + 1)*y.

%F (End)

%e O.g.f.: A(x) = 1 + 2*x + 10*x^2 + 56*x^3 + 346*x^4 + 2252*x^5 + ...

%e O.g.f.: A(x) = 1/(1-2*x) + 3!*x^2/(1-2*x)^4 + (6!/2!^3)*x^4/(1-2*x)^7 + (9!/3!^3)*x^6/(1-2*x)^10 + (12!/4!^3)*x^8/(1-2*x)^13 + ... - _Paul D. Hanna_, Oct 30 2010

%e Let g.f. A(x) = Sum_{n >= 0} a(n)*x^n/n!^3, then

%e A(x) = 1 + 2*x + 10*x^2/2!^3 + 56*x^3/3!^3 + 346*x^4/4!^3 + ... where

%e A(x) = [1 + x + x^2/2!^3 + x^3/3!^3 + x^4/4!^3 + ...]^2. - _Paul D. Hanna_

%p A000172 := proc(n)

%p add(binomial(n,k)^3,k=0..n) ;

%p end proc:

%p seq(A000172(n),n=0..10) ; # _R. J. Mathar_, Jul 26 2014

%p A000172_list := proc(len) series(hypergeom([], [1, 1], x)^2, x, len);

%p seq((n!)^3*coeff(%, x, n), n=0..len-1) end:

%p A000172_list(21); # _Peter Luschny_, May 31 2017

%t Table[Sum[Binomial[n,k]^3,{k,0,n}],{n,0,30}] (* _Harvey P. Dale_, Aug 24 2011 *)

%t Table[ HypergeometricPFQ[{-n, -n, -n}, {1, 1}, -1], {n, 0, 20}] (* _Jean-François Alcover_, Jul 16 2012, after symbolic sum *)

%t a[n_] := Sum[ Binomial[2k, n]*Binomial[2k, k]*Binomial[2(n-k), n-k], {k, 0, n}]/2^n; Table[a[n], {n, 0, 20}] (* _Jean-François Alcover_, Mar 20 2013, after _Zhi-Wei Sun_ *)

%t a[ n_] := SeriesCoefficient[ Hypergeometric2F1[ 1/3, 2/3, 1, 27 x^2 / (1 - 2 x)^3] / (1 - 2 x), {x, 0, n}]; (* _Michael Somos_, Jul 16 2014 *)

%o (PARI) {a(n)=polcoeff(sum(m=0,n,(3*m)!/m!^3*x^(2*m)/(1-2*x+x*O(x^n))^(3*m+1)),n)} \\ _Paul D. Hanna_, Oct 30 2010

%o (PARI) {a(n)=n!^3*polcoeff(sum(m=0,n,x^m/m!^3+x*O(x^n))^2,n)} \\ _Paul D. Hanna_, Jan 19 2011

%o (Haskell)

%o a000172 = sum . map a000578 . a007318_row

%o -- _Reinhard Zumkeller_, Jan 06 2013

%o (Sage)

%o def A000172():

%o x, y, n = 1, 2, 1

%o while true:

%o yield x

%o n += 1

%o x, y = y, (8*(n-1)^2*x + (7*n^2-7*n + 2)*y) / n^2

%o a = A000172()

%o [a.next() for i in range(21)] # _Peter Luschny_, Oct 12 2013

%o (PARI) A000172(n)={sum(k=0,(n-1)\2,binomial(n,k)^3)*2+if(!bittest(n,0),binomial(n,n\2)^3)} \\ _M. F. Hasler_, Sep 21 2015

%Y Cf. A002893, A052144, A005260, A096191, A033581, A189791. Second row of array A094424.

%Y Cf. A181543, A006480, A141057, A000578, A007318.

%Y The Apéry-like numbers [or Apéry-like sequences, Apery-like numbers, Apery-like sequences] include A000172, A000984, A002893, A002895, A005258, A005259, A005260, A006077, A036917, A063007, A081085, A093388, A125143 (apart from signs), A143003, A143007, A143413, A143414, A143415, A143583, A183204, A214262, A219692,A226535, A227216, A227454, A229111 (apart from signs), A260667, A260832, A262177, A264541, A264542, A279619, A290575, A290576. (The term "Apery-like" is not well-defined.)

%Y For primes that do not divide the terms of the sequences A000172, A005258, A002893, A081085, A006077, A093388, A125143, A229111, A002895, A290575, A290576, A005259 see A260793, A291275-A291284 and A133370 respectively.

%K nonn,easy,nice

%O 0,2

%A _N. J. A. Sloane_

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Last modified November 15 01:00 EST 2019. Contains 329142 sequences. (Running on oeis4.)