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 A072409 #20 Oct 06 2018 03:56:35 %S A072409 1,1634,2178,6514,8208,9474 %N A072409 4th-order digital invariants: the sum of the 4th power of the digits of n equals some number k and the sum of the 4th power of the digits of k equals n. %D A072409 David Wells, Penguin Dictionary of Curious and Interesting Numbers, Revised Edition, London, England, 1997, p. 155&153. %e A072409 2178 is included because 2^4 + 1^4 + 7^4 + 8^4 = 6514 and 6^4 + 5^4 + 1^4 + 4^4 = 2178. %t A072409 f[n_] := Apply[Plus, IntegerDigits[Apply[Plus, IntegerDigits[n]^4]]^4]; Select[ Range[10^7], f[ # ] == # &] %K A072409 nonn,fini,full,base %O A072409 1,2 %A A072409 _Harvey P. Dale_, Jul 31 2002 %E A072409 Edited by _Robert G. Wilson v_, Aug 09 2002