OFFSET
1,1
LINKS
Max Alekseyev, Table of n, a(n) for n = 1..690
FORMULA
EXAMPLE
a(2)=10 because 9^2-1 has divisors {1, 2, 4, 5, 8, 10, 16, 20, 40, 80}.
MAPLE
a:=n->numtheory[tau](9^n-1):
seq(a(n), n=1..100);
MATHEMATICA
DivisorSigma[0, 9^Range[100]-1]
PROG
(PARI) a(n) = numdiv(9^n-1);
CROSSREFS
KEYWORD
nonn
AUTHOR
Sean A. Irvine, Oct 15 2023
STATUS
approved