OFFSET
1,3
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
EXAMPLE
For n=2, sigma(sigma(n)) = 4, so a(2) = 1.
MAPLE
seq(denom((numtheory:-sigma@@2)(n)/n), n=1..200); # Robert Israel, Aug 15 2018
MATHEMATICA
Table[(DivisorSigma[1, DivisorSigma[1, n]])/n, {n, 70}]//Denominator (* Harvey P. Dale, Mar 30 2023 *)
PROG
(PARI) a(n) = denominator(sigma(sigma(n))/n);
CROSSREFS
KEYWORD
nonn,frac
AUTHOR
Michel Marcus, Aug 14 2018
STATUS
approved