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

Terms

a(0) =1a(1) =5a(2) =205a(3) =168305a(4) =2084645a(5) =37217545a(6) =1711493545a(7) =2483072545a(8) =2763736405a(9) =8866165745a(10) =30555604445a(11) =55328770405a(12) =169592124685a(13) =378465215105a(14) =423977184745