A180709 a(n) = sigma(n*a(n-1)) for n>1 with a(1)=1.

1, 3, 13, 98, 1026, 16940, 318402, 8751951, 138772480, 4323245864, 120795955200, 5325759445800, 253615827548160, 17175333492928512, 1074413211620474880, 76931332113306746880, 5820049307236627906560, 433263727052606574415872

Offset

1,2

Links

Table of n, a(n) for n=1..18.

Mathematica

nxt[{n_, a_}]:={n+1, DivisorSigma[1, a(n+1)]}; NestList[nxt, {1, 1}, 20][[All, 2]] (* Harvey P. Dale, Apr 28 2018 *)

Prog

(PARI) a(n)=if(n==1, 1, sigma(n*a(n-1)))

Crossrefs

Cf. A119791.

Sequence in context: A144276 A083770 A084725 * A125207 A352300 A306082

Adjacent sequences: A180706 A180707 A180708 * A180710 A180711 A180712

Keyword

nonn

Author

Paul D. Hanna, Sep 18 2010

Status

approved