A180710 a(n) = sigma(2^(n-1)*a(n-1)) for n>1 with a(1)=1.

1, 3, 28, 504, 26520, 3090528, 690908400, 432222336000, 543025101265920, 1255553120600064000, 6002949274226395545600, 65900815978203369461760000, 1290586365875976383280969154560, 48847915039427778415352397535641600

Offset

1,2

Comments

Conjecture: sigma(n) | a(n) for n>=1.

Links

Table of n, a(n) for n=1..14.

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

Sequence in context: A327114 A327336 A355473 * A005328 A192559 A161971

Adjacent sequences: A180707 A180708 A180709 * A180711 A180712 A180713

Keyword

nonn

Author

Paul D. Hanna, Sep 18 2010

Status

approved