A077315 - OEIS

3, 7, 31, 43, 127, 241, 967, 5323, 8191, 117127, 131071, 524287, 7496191, 10307263, 77948683, 253755391, 428717761, 738197503, 1714871047, 2147483647, 16240345087, 27437936767, 42218553343, 1965081755647, 2414538435583, 7024111812607, 7860327022591, 16630113370111