OFFSET
1,2
COMMENTS
Number of terms < 10^k: 1, 5, 8, 15, 26, 46, 71, 105, 160, 228, ..., . Robert G. Wilson v, Jan 10 2018
LINKS
Robert G. Wilson v, Table of n, a(n) for n = 1..229 (first 99 terms from G. C. Greubel)
MATHEMATICA
Select[ Range[ 335000], Mod[ #^2 - 1, EulerPhi[ # ]] == 0 && !PrimeQ[ # ] &]
PROG
(PARI) isok(n) = !isprime(n) && !((n^2-1) % eulerphi(n)); \\ Michel Marcus, Jan 11 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
Leroy Quet and Robert G. Wilson v, Sep 01 2004
STATUS
approved