a(n) is the smallest k > n such that 2^(k-n) == 1 (mod k).

Terms

a(0) =1a(1) =3a(2) =20737a(3) =9a(4) =7a(5) =25a(6) =31a(7) =15a(8) =127a(9) =17a(10) =73a(11) =15a(12) =23a(13) =33a(14) =3479a(15) =21a(16) =31a(17) =65a(18) =131071a(19) =51a(20) =524287a(21) =31a(22) =127a(23) =33a(24) =47a(25) =69a(26) =31a(27) =39a(28) =49a(29) =43