OFFSET
1,1
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
Eric Weisstein's World of Mathematics, Cubefree.
FORMULA
a(n) = A007948(n) + 1.
Dirichlet g.f.: zeta(s) * (1 + Product_{p prime} (1 + 1/p^(s-1) - 1/p^s + 1/p^(2*s-2) - 1/p^(2*s-1)). - Amiram Eldar, Feb 01 2024
MATHEMATICA
f[p_, e_] := p^Min[e, 2]; a[1] = 2; a[n_] := 1 + Times @@ f @@@ FactorInteger[n]; Array[a, 100] (* Amiram Eldar, Feb 01 2024 *)
PROG
(PARI) a(n) = {my(f = factor(n)); 1 + prod(i = 1, #f~, f[i, 1]^min(f[i, 2], 2)); } \\ Amiram Eldar, Feb 01 2024
CROSSREFS
KEYWORD
nonn
AUTHOR
Reinhard Zumkeller, Aug 11 2004
STATUS
approved