Numbers k such that k^2 divides 4^k-1.

Terms

a(0) =1a(1) =3a(2) =21a(3) =903a(4) =2667a(5) =7077a(6) =113799a(7) =114681a(8) =304311a(9) =389193a(10) =898779a(11) =932799a(12) =4893357a(13) =6099429a(14) =8131683a(15) =8776257a(16) =14452473a(17) =38350263a(18) =38647497a(19) =40647747a(20) =49427511a(21) =99583113a(22) =118465473a(23) =128794323a(24) =131158041a(25) =152643813a(26) =262275447a(27) =300510651a(28) =314353263a(29) =335873559