Nearest-neighbors of perfect numbers.

Terms

a(0) =5a(1) =7a(2) =27a(3) =29a(4) =495a(5) =497a(6) =8127a(7) =8129a(8) =33550335a(9) =33550337a(10) =8589869055a(11) =8589869057a(12) =137438691327a(13) =137438691329