A380831 Numbers k such that k^(k + 1) == k + 1 (mod 2*k + 1) while 2*k+1 is not prime.

1023, 1638, 14670, 21399, 24570, 40290, 44178, 45375, 52326, 98046, 128499, 135975, 157410, 229494, 244998, 257223, 370875, 400302, 419430, 436590, 458163, 502326, 625974, 686826, 754854, 839270, 905786, 993510, 1102983, 1134546, 1142226, 1152083, 1193898, 1373238, 1374011

Offset: 1

Author

Michel Marcus, Feb 05 2025

Keywords

• nonn

Crossrefs

Intersection of A374913 and A047845.

Programs

PARI

isok(k) = (!isprime(2*k+1)) && (Mod(k, 2*k+1)^(k+1) == k+1);