OFFSET
1,2
COMMENTS
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..1000
MATHEMATICA
Nest[DivisorSigma[1, #]&, Range[60], 4] (* Harvey P. Dale, Oct 05 2011 *)
PROG
(Magma) [ SumOfDivisors(SumOfDivisors(SumOfDivisors(SumOfDivisors(n)))) : n in [1..100]];
(PARI) a(n) = sigma(sigma(sigma(sigma(n)))); \\ Michel Marcus, Apr 29 2017
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Jonathan Vos Post, May 27 2007
STATUS
approved