OFFSET
1,2
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
FORMULA
For n=2, sigma(sigma(n)) = 4, so a(2) = 2.
EXAMPLE
Fractions begin with 1, 2, 7/3, 2, 12/5, 14/3, 15/7, 3, 14/9, 39/10, 28/11, 14/3, ...
MAPLE
seq(numer((numtheory:-sigma@@2)(n)/n), n=1..100); # Robert Israel, Aug 14 2018
MATHEMATICA
a[n_] := Numerator[DivisorSigma[1, DivisorSigma[1, n]]/n]; Array[a, 100] (* Amiram Eldar, Apr 04 2024 *)
PROG
(PARI) a(n) = numerator(sigma(sigma(n))/n);
CROSSREFS
KEYWORD
nonn,frac
AUTHOR
Michel Marcus, Aug 14 2018
STATUS
approved