OFFSET
1,2
LINKS
Álvar Ibeas, Table of n, a(n) for n = 1..10000
FORMULA
a(n) = n^3 * Sum_{d^3 | n} (moebius(d) / d^6).
Multiplicative with a(p) = p^3; a(p^2) = p^6; a(p^e) = p^(3e) - p^(3e-6), for e > 2.
Sum_{k=1..n} a(k) ~ n^4 / (4*Zeta(9)). - Vaclav Kotesovec, Feb 03 2019
Sum_{k>=1} 1/a(k) = Product_{p prime} (1 + 1/p^3 + 1/p^6 + 1/((p^3 - 1)^2*(p^3 + 1))) = 1.202094253239358480267688474077353358147971390519883358936462981705245... - Vaclav Kotesovec, Sep 26 2020
PROG
(PARI) a(n) = n^3*sumdiv(n, d, if (ispower(d, 3), moebius(sqrtnint(d, 3))/d^2)); \\ Michel Marcus, Feb 10 2015
(PARI) for(n=1, 100, print1(direuler(p=2, n, 1/(1 - p^3*X)*(1 - p^3*X^3))[n], ", ")) \\ Vaclav Kotesovec, Sep 26 2020
CROSSREFS
KEYWORD
mult,nonn
AUTHOR
Álvar Ibeas, Jan 31 2015
STATUS
approved