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 A058696 Number of ways to partition 2n into positive integers. 54
 1, 2, 5, 11, 22, 42, 77, 135, 231, 385, 627, 1002, 1575, 2436, 3718, 5604, 8349, 12310, 17977, 26015, 37338, 53174, 75175, 105558, 147273, 204226, 281589, 386155, 526823, 715220, 966467, 1300156, 1741630, 2323520, 3087735, 4087968 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS A bisection of A000041, the other one is A058695. Ramanujan theta functions: f(q) (see A121373), phi(q) (A000122), psi(q) (A010054), chi(q) (A000700). - Michael Somos, Feb 16 2014 a(n) = number of partitions of 3n-2 having n as a part, for n >= 1.  Also, a(n+1) is the number of partitions of 3n having n as a part, for n >= 1.  - Clark Kimberling, Mar 02 2014 REFERENCES Roland Bacher, P De La Harpe, Conjugacy growth series of some infinitely generated groups. 2016. hal-01285685v2; https://hal.archives-ouvertes.fr/hal-01285685/document LINKS Seiichi Manyama, Table of n, a(n) for n = 0..10000 K. Blum, Bounds on the Number of Graphical Partitions, arXiv:2103.03196 [math.CO], 2021. See Table on p. 7. Michael Somos, Introduction to Ramanujan theta functions Eric Weisstein's World of Mathematics, Ramanujan Theta Functions FORMULA Expansion of f(x^3, x^5) / f(-x)^2 in powers of x where f() is a Ramanujan theta function. - Michael Somos, Feb 16 2014 Euler transform of period 16 sequence [ 2, 2, 3, 2, 3, 1, 2, 1, 2, 1, 3, 2, 3, 2, 2, 1, ...]. - Michael Somos,  Apr 25 2003 a(n) = A000041(2*n). Convolution of A000041 and A035294. - Michael Somos, Feb 16 2014 G.f.: Product_{k>=1} (1 + x^(8*k-4)) * (1 + x^(8*k)) * (1 + x^k)^2 / ((1 + x^(8*k-1)) * (1 + x^(8*k-7)) * (1 - x^k)). - Vaclav Kotesovec, Nov 17 2016 EXAMPLE G.f. = 1 + 2*x + 5*x^2 + 11*x^3 + 22*x^4 + 42*x^5 + 77*x^6 + 135*x^7 + ... G.f. = q^-1 + 2*q^47 + 5*q^95 + 11*q^143 + 22*q^191 + 42*q^239 + 77*q^287 + ... MAPLE a:= n-> combinat[numbpart](2*n): seq(a(n), n=0..42);  # Alois P. Heinz, Jan 29 2020 MATHEMATICA nn=100; Table[CoefficientList[Series[Product[1/(1-x^i), {i, 1, nn}], {x, 0, nn}], x][[2i-1]], {i, 1, nn/2}] (* Geoffrey Critzer, Sep 28 2013 *) (* also *) Table[PartitionsP[2 n], {n, 0, 40}] (* Clark Kimberling, Mar 02 2014 *) (* also *) Table[Count[IntegerPartitions[3 n - 2], p_ /; MemberQ[p, n]], {n, 20}]   (* Clark Kimberling, Mar 02 2014 *) nmax = 60; CoefficientList[Series[Product[(1 + x^(8*k-4))*(1 + x^(8*k))*(1 + x^k)^2/((1 + x^(8*k-1))*(1 + x^(8*k-7))*(1 - x^k)), {k, 1, nmax}], {x, 0, nmax}], x] (* Vaclav Kotesovec, Nov 17 2016 *) PROG (PARI) {a(n) = if( n<0, 0, polcoeff( 1 / eta(x + O(x^(2*n + 1))), 2*n))}; /* Michael Somos, Apr 25 2003 */ (PARI) a(n) = numbpart(2*n); \\ Michel Marcus, Sep 28 2013 (MuPAD) combinat::partitions::count(2*i) \$i=0..54 // Zerinvary Lajos, Apr 16 2007 CROSSREFS Cf. A000041, A035294, A058695. Sequence in context: A290778 A291590 A236430 * A134508 A091357 A309950 Adjacent sequences:  A058693 A058694 A058695 * A058697 A058698 A058699 KEYWORD nonn AUTHOR N. J. A. Sloane, Dec 31 2000 STATUS approved

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Last modified April 15 14:19 EDT 2021. Contains 342977 sequences. (Running on oeis4.)