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A396090
Number of integer partitions of 2*n with reverse-alternating sum 6.
0
0, 0, 0, 1, 1, 3, 6, 12, 21, 38, 62, 103, 163, 257, 392, 596, 882, 1299, 1879, 2699, 3823, 5382, 7488, 10357, 14191, 19331, 26126, 35124, 46895, 62306, 82291, 108189, 141492, 184273, 238857, 308411, 396537, 508003, 648309, 824601, 1045147, 1320559, 1663176, 2088589, 2615020
OFFSET
0,6
LINKS
FORMULA
G.f.: (Product_{k>0} 1/(1-q^k)) * B(q), where B(q) is the g.f. of A395257.
a(n) = Sum_{k=0..n} A395257(k) * A000041(n-k).
a(n) ~ 3*n^(3/2) * exp(Pi*sqrt(2*n/3)) / (5*2^(5/2)*Pi^5). - Vaclav Kotesovec, May 20 2026
MATHEMATICA
nmax = 50; With[{k = 3}, colk = CoefficientList[Series[Sum[(-1)^(i-1) * x^(i*(i-1)/2 + k)/Product[(1 - x^j), {j, 1, 2*k - i}], {i, 1, 2*k} ], {x, 0, nmax}], x]]; Table[Sum[colk[[k+1]]*PartitionsP[n-k], {k, 0, n}], {n, 0, nmax}] (* Vaclav Kotesovec, May 20 2026 *)
PROG
(PARI) my(N=50, q='q+O('q^N)); concat([0, 0, 0], Vec(1/prod(k=1, N, 1-q^k)*sum(j=1, 6, (-1)^(j-1)*q^(j*(j-1)/2+3)/prod(k=1, 6-j, 1-q^k))))
CROSSREFS
Column k=3 of A344610.
Sequence in context: A247662 A337462 A215005 * A396091 A006330 A293636
KEYWORD
nonn,new
AUTHOR
Seiichi Manyama, May 17 2026
STATUS
approved