OFFSET
1,1
LINKS
Donovan Johnson, Table of n, a(n) for n = 1..500
Richard K. Guy, Divisors and desires, Amer. Math. Monthly, 104 (1997), 359-360.
PROG
(PARI) isok(n) = !isprime(n) && issquare(eulerphi(n)*sigma(n)+1); \\ Michel Marcus, Oct 02 2017
CROSSREFS
KEYWORD
nonn
AUTHOR
EXTENSIONS
Offset corrected by Donovan Johnson, Apr 02 2012
STATUS
approved