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
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Sep 18 2010
STATUS
approved