OFFSET
0,3
LINKS
Matthew Campbell and Charles R Greathouse IV, Table of n, a(n) for n = 0..1866 (terms 0..677 from Campbell)
EXAMPLE
a(2) = sigma(0, hyperfactorial(2)) = sigma(0, 2^2*1^1) = sigma(0, 4). The divisors of 4 are 1, 2, and 4. The number of divisors is a(2) = 3.
MATHEMATICA
Table[DivisorSigma[0, Hyperfactorial[n]], {n, 0, 200}]
PROG
(PARI) hf(n, p)=my(s); forstep(k=p, n, p, s+=k); if(n<p^2, s, p*hf(n\p, p)+s)
a(n)=factorback(apply(p->hf(n, p)+1, primes([2, n]))) \\ Charles R Greathouse IV, Jul 17 2015
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Matthew Campbell, Jul 17 2015
STATUS
approved