OFFSET
1,2
COMMENTS
Conjecture: sigma(n) | a(n) for n>=1.
MATHEMATICA
nxt[{a_, b_}]:={a+1, DivisorSigma[1, 2^a*b]}; Transpose[NestList[nxt, {1, 1}, 20]][[2]] (* Harvey P. Dale, Oct 02 2012 *)
PROG
(PARI) a(n)=if(n==1, 1, sigma(2^(n-1)*a(n-1)))
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Sep 18 2010
STATUS
approved