OFFSET
1,2
COMMENTS
Dirichlet inverse of the positive triangular numbers A000217.
LINKS
Vaclav Kotesovec, Table of n, a(n) for n = 1..10000
FORMULA
G.f. A(x) satisfies: A(x) = x - Sum_{k>=2} A000217(k) * A(x^k).
Dirichlet g.f.: 2 / (zeta(s-1) + zeta(s-2)).
MATHEMATICA
a[n_] := If[n == 1, n, -(1/2) Sum[If[d > 1, d (d + 1) a[n/d], 0], {d, Divisors[n]}]]; Table[a[n], {n, 55}]
PROG
(PARI) lista(nn) = {my(va=vector(nn)); va[1] = 1; for (n=2, nn, va[n] = -sumdiv(n, d, if (d>1, d*(d + 1)*va[n/d]))/2; ); va; } \\ Michel Marcus, May 15 2020
CROSSREFS
KEYWORD
sign
AUTHOR
Ilya Gutkovskiy, May 14 2020
STATUS
approved