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A363607
Expansion of Sum_{k>0} x^(3*k)/(1-x^k)^4.
7
0, 0, 1, 4, 10, 21, 35, 60, 85, 130, 165, 245, 286, 399, 466, 620, 680, 921, 969, 1274, 1366, 1705, 1771, 2325, 2310, 2886, 3010, 3679, 3654, 4666, 4495, 5580, 5622, 6664, 6590, 8285, 7770, 9405, 9426, 11210, 10660, 13230, 12341, 14953, 14740, 16951, 16215, 20181
OFFSET
1,4
LINKS
FORMULA
G.f.: Sum_{k>0} binomial(k,3) * x^k/(1 - x^k).
a(n) = Sum_{d|n} binomial(d,3).
MATHEMATICA
a[n_] := DivisorSum[n, Binomial[#, 3] &]; Array[a, 50] (* Amiram Eldar, Jul 25 2023 *)
PROG
(PARI) my(N=50, x='x+O('x^N)); concat([0, 0], Vec(sum(k=1, N, x^(3*k)/(1-x^k)^4)))
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Seiichi Manyama, Jun 11 2023
STATUS
approved