Numbers k such that 2^k == -1 (mod k-1).

Terms

a(0) =2a(1) =6a(2) =66a(3) =378a(4) =1190a(5) =1470a(6) =25806a(7) =58590a(8) =134946a(9) =137346a(10) =170586a(11) =272610a(12) =285390a(13) =420210a(14) =538734a(15) =592410a(16) =618450a(17) =680706a(18) =778806a(19) =1163066a(20) =1520442a(21) =1700946a(22) =2099202a(23) =2831010a(24) =4020030a(25) =4174170a(26) =4516110a(27) =5059890a(28) =5215770