10 for N=2 to 10000000
20 P=modpow(2,N,N)
30 if (P+2) @ N=0 then print N
40 next
finds
2
6
66
946
8646
180246
199606
265826
383846
1234806
3757426
9880278
which allows finding Sloane's A006517 in the OEIS. It's an infinite sequence.

Posted by Charlie
on 20130912 15:46:20 