OFFSET
1,1
LINKS
Max Alekseyev, Table of n, a(n) for n = 1..690
FORMULA
MATHEMATICA
EulerPhi[9^Range[30] - 1]
PROG
(PARI) {a(n) = eulerphi(9^n-1)}
CROSSREFS
KEYWORD
nonn
AUTHOR
Sean A. Irvine, Oct 15 2023
STATUS
approved