OFFSET
1,1
LINKS
Max Alekseyev, Table of n, a(n) for n = 1..1122
FORMULA
EXAMPLE
a(4)=8 because 4^4-1 has divisors {1, 3, 5, 15, 17, 51, 85, 255}.
MAPLE
a:=n->numtheory[tau](4^n-1):
seq(a(n), n=1..100);
MATHEMATICA
DivisorSigma[0, 4^Range[100]-1] (* Paolo Xausa, Oct 14 2023 *)
PROG
(PARI) a(n) = numdiv(4^n-1);
CROSSREFS
KEYWORD
nonn
AUTHOR
Sean A. Irvine, Oct 14 2023
STATUS
approved