Numbers k such that 4^k == -1 (mod k-1).

Terms

a(0) =2a(1) =18a(2) =4098a(3) =7362a(4) =85074a(5) =658530a(6) =3999138a(7) =72281282a(8) =285143058a(9) =628944690a(10) =854112114a(11) =1423081170a(12) =2561019282a(13) =3111576930a(14) =4298117634a(15) =5921265042a(16) =14224884930a(17) =21336998130a(18) =34317377234a(19) =50723421714a(20) =63797137890a(21) =144269032050a(22) =163834314354a(23) =187397322210a(24) =212565453282a(25) =231286579794a(26) =232992827298a(27) =266198715090a(28) =314834584482a(29) =348160787730