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]