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 A225866 #8 May 19 2013 00:10:54 %S A225866 1,3,5,33,60,245,304,372,1265,1568,1756,1799,1856,2409,2532,2976,3100, %T A225866 3281,3376,3394,3813,5637,5972,6147,6538,7213,7299,7896,7966,8371, %U A225866 10419,11526,13411,13856,14168,15024,15283,15709,16506,16577,16916,19212,19829,21372 %N A225866 Numbers n such that the sum of the numbers in the Collatz (3x+1) iteration of n is a perfect square. %H A225866 Donovan Johnson, <a href="/A225866/b225866.txt">Table of n, a(n) for n = 1..1000</a> %e A225866 60 is in the sequence because 60 + 30 + 15 + 46 + 23 + 70 + 35 + 106 + 53 + 160 + 80 + 40 + 20 + 10 + 5 + 16 + 8 + 4 + 2 + 1 = 784 = 28^2. %t A225866 collatz[n_] := NestWhileList[If[EvenQ[#], #/2, 3#+1]&, n, #>1&]; Select[Range[22000], IntegerQ[Sqrt[Total[collatz[#]]]]&] %Y A225866 Cf. A033493. %K A225866 nonn %O A225866 1,2 %A A225866 _Michel Lagneau_, May 18 2013