OFFSET
0,4
LINKS
Seiichi Manyama, Table of n, a(n) for n = 0..5000
FORMULA
G.f.: exp(Sum_{k>=1} ( Sum_{d|k} d*(d^(k/d) - 1) ) * x^k/k).
From Vaclav Kotesovec, Sep 27 2018: (Start)
a(n) ~ c * 3^(n/3), where
c = 4613.026226899587659466790384528262900057997961519... if mod(n,3)=0
c = 4612.491093385908314202944836907761153110706939289... if mod(n,3)=1
c = 4612.543916007416515763773288072302642108310934844... if mod(n,3)=2
(End)
MAPLE
a:=series(mul((1-x^k)/(1-k*x^k), k=1..100), x=0, 41): seq(coeff(a, x, n), n=0..40); # Paolo P. Lava, Apr 02 2019
MATHEMATICA
nmax = 40; CoefficientList[Series[Product[(1 - x^k)/(1 - k*x^k), {k, 1, nmax}], {x, 0, nmax}], x]
nmax = 40; CoefficientList[Series[Exp[Sum[Sum[d (d^(k/d) - 1), {d, Divisors[k]}] x^k/k, {k, 1, nmax}]], {x, 0, nmax}], x]
a[n_] := a[n] = If[n == 0, 1, Sum[Sum[d (d^(k/d) - 1), {d, Divisors[k]}] a[n - k], {k, 1, n}]/n]; Table[a[n], {n, 0, 40}]
PROG
(PARI) x='x+O('x^40); Vec(prod(n=1, 40, (1-x^n)/(1-n*x^n))) \\ Altug Alkan, Sep 27 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Sep 27 2018
STATUS
approved