A069972 a(n) = Sum_{d|2*n,d+1|2*n} d.

1, 1, 3, 1, 1, 6, 1, 1, 3, 5, 1, 6, 1, 1, 8, 1, 1, 6, 1, 5, 9, 1, 1, 6, 1, 1, 3, 8, 1, 15, 1, 1, 3, 1, 1, 14, 1, 1, 3, 5, 1, 12, 1, 1, 17, 1, 1, 6, 1, 5, 3, 1, 1, 6, 11, 8, 3, 1, 1, 15, 1, 1, 9, 1, 1, 17, 1, 1, 3, 5, 1, 14, 1, 1, 8, 1, 1, 18, 1, 5, 3, 1, 1, 19, 1, 1, 3, 1, 1, 24, 14, 1, 3, 1, 1, 6, 1, 1

Offset: 1

Author

Vladeta Jovovic, Apr 29 2002

Keywords

• easy
• nonn

Links

• Antti Karttunen, Table of n, a(n) for n = 1..20000

Crossrefs

Cf. A007862.

Programs

PARI

A069972(n) = { n = 2*n; sumdiv(n,d,if(!(n%(1+d)), d, 0)); }; \\ Antti Karttunen, Mar 02 2023

Formula

G.f.: (conjectured) Sum_{n>=1} n*x^(n*(n+1)/2)/(1-x^(n*(n+1)/2)). - Joerg Arndt, Jan 30 2011