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A363898
Expansion of Sum_{k>0} k * x^(2*k) / (1 - x^(5*k)).
5
0, 1, 0, 2, 0, 3, 1, 4, 0, 5, 0, 7, 0, 9, 0, 8, 1, 9, 0, 10, 3, 12, 0, 14, 0, 13, 1, 18, 0, 15, 0, 17, 0, 19, 5, 21, 1, 19, 0, 20, 0, 28, 0, 24, 0, 23, 1, 28, 7, 25, 3, 27, 0, 29, 0, 36, 1, 29, 0, 35, 0, 32, 9, 34, 0, 36, 1, 38, 0, 45, 0, 43, 0, 39, 0, 38, 12, 39, 0, 40, 3, 42, 0, 63, 5, 43, 1
OFFSET
1,4
LINKS
FORMULA
a(n) = Sum_{d|n, n/d==2 mod 5} d.
G.f.: Sum_{k>0} x^(5*k-3) / (1 - x^(5*k-3))^2.
MATHEMATICA
a[n_] := DivisorSum[n, # &, Mod[n/#, 5] == 2 &]; Array[a, 100] (* Amiram Eldar, Jun 27 2023 *)
PROG
(PARI) a(n) = sumdiv(n, d, (n/d%5==2)*d);
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Jun 27 2023
STATUS
approved