OFFSET
1,2
LINKS
Antti Karttunen, Table of n, a(n) for n = 1..10000
FORMULA
a(p) = 3, for primes p.
a(n) = 2*A000005(n) - 1. - Vladeta Jovovic, Sep 13 2006
Equals A051731 * [1, 2, 2, 2, ...]. - Gary W. Adamson, Sep 21 2007
G.f.: Sum_{n>0} x^n*(1+x^n)/(1-x^n). - Franklin T. Adams-Watters, Oct 09 2009
MATHEMATICA
Table[2 DivisorSigma[0, n]-1, {n, 97}] (* Stefano Spezia, Sep 08 2023 *)
PROG
(PARI) N=66; x='x+O('x^N); /* that many terms */
Vec(sum(n=1, N, x^n*(1+x^n)/(1-x^n))) /* show terms */ /* Joerg Arndt, May 25 2011 */
(PARI) A114003(n) = (2*numdiv(n))-1; \\ After Jovovic's formula. Antti Karttunen, May 25 2017
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul Barry, Nov 12 2005
STATUS
approved