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 A050001 #13 Jul 13 2013 12:02:14 %S A050001 1,5,2,4,19,6,16,26,3,18,23,28,10,15,20,25,61,7,12,35,17,22,76,27,45, %T A050001 130,9,14,135,37,73,91,24,60,127,29,47,65,11,34,52,70,88,478,21,75, %U A050001 124,93,359,44,62,129,594,8,49,116,13,134,506,36,54,431,72,90,139,480,41,59 %N A050001 a(n)=position of n in A050000. %C A050001 Inverse permutation to A050000: a(A050000(n)) = A050000(a(n)) = n. %H A050001 Reinhard Zumkeller, <a href="/A050001/b050001.txt">Table of n, a(n) for n = 1..10000</a> %H A050001 <a href="/index/Per#IntegerPermutation">Index entries for sequences that are permutations of the natural numbers</a> %o A050001 (Haskell) %o A050001 import Data.List (elemIndex) %o A050001 import Data.Maybe (fromJust) %o A050001 a050001 n = (fromJust $ elemIndex n a050000_list) + 1 %o A050001 -- _Reinhard Zumkeller_, Nov 13 2011 %Y A050001 a(n) = k <=> A050000(k) = n. %K A050001 nonn,easy %O A050001 1,2 %A A050001 _Clark Kimberling_ %E A050001 More terms from _Ray Chandler_, Nov 16 2003