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A180707 a(n) = sigma(2*a(n-1)) for n>1 with a(1)=1. 1
1, 3, 12, 60, 360, 2418, 12544, 58311, 299520, 2235324, 14515200, 122882760, 1152592896, 8365593600, 81041688000, 812657664000, 8244072345600, 78851793162240, 701965262389248, 5040363458592000, 49476663690854400 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..21.

MATHEMATICA

NestList[DivisorSigma[1, 2#]&, 1, 20] (* Harvey P. Dale, Jan 12 2018 *)

PROG

(PARI) a(n)=if(n==1, 1, sigma(2*a(n-1)))

CROSSREFS

Sequence in context: A000258 A326242 A070863 * A062569 A089057 A077134

Adjacent sequences:  A180704 A180705 A180706 * A180708 A180709 A180710

KEYWORD

nonn

AUTHOR

Paul D. Hanna, Sep 18 2010

STATUS

approved

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Last modified August 10 19:52 EDT 2020. Contains 336381 sequences. (Running on oeis4.)