A180708 a(n) = sigma(3*a(n-1)) for n>1 with a(1)=1.

1, 4, 28, 224, 2016, 20160, 243840, 2545920, 30905280, 388908036, 3622707200, 44117911764, 387754160640, 5065246517760, 67333642371072, 829993839244416, 9887956143636480, 150394118343146496, 1797812804753817600

Offset

1,2

Links

Paul D. Hanna, Table of n, a(n) for n = 1..300

Mathematica

NestList[DivisorSigma[1, 3#]&, 1, 20] (* Harvey P. Dale, Aug 18 2023 *)

Prog

(PARI) a(n)=if(n==1, 1, sigma(3*a(n-1)))

Crossrefs

Cf. A180707.

Sequence in context: A121203 A368234 A192620 * A370187 A191094 A220876

Adjacent sequences: A180705 A180706 A180707 * A180709 A180710 A180711

Keyword

nonn

Author

Paul D. Hanna, Sep 18 2010

Status

approved