This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A337261 #18 Aug 25 2020 06:39:41 %S A337261 0,1,2,3,8,9,11,12 %N A337261 Numbers k such that the digits of 4^k cannot be rearranged to form the digits of t^2, for t not a power of 2. %C A337261 Leading zeros are not allowed. %C A337261 2^odd cannot be rearranged to a square number: odd powers of 2 are congruent to 2,5,8 mod 9; squares are congruent to 0,1,4,7 mod 9; and rearranging preserves the mod-9 value. %C A337261 If it exists, a(9) > 78. %D A337261 Don Reble, Posting to Sequence Fans Mailing List, Aug 21 2020 %e A337261 4 is not here because 4^4 = 256 -> 625 = 25^2. %e A337261 10 is not here, because 4^10 = 1048576 -> 1056784 = 1028^2. %e A337261 11 is here, even though 4^11 = 4194304 -> 0413449 = 643^2, because leading zeros aren't allowed. %Y A337261 Cf. A000302 (powers of 4), A337252. %K A337261 nonn,base,more %O A337261 1,3 %A A337261 _N. J. A. Sloane_, Aug 22 2020