OFFSET
1,2
EXAMPLE
7361 is a term because 7361 = 17*433 divides 2^psi(7361) + 1 = 2^(18*434) + 1.
PROG
(PARI) a001615(n) = n*sumdivmult(n, d, issquarefree(d)/d);
is(n) = Mod(2, n)^a001615(n)==-1;
CROSSREFS
KEYWORD
nonn
AUTHOR
Altug Alkan, Aug 19 2017
STATUS
approved