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 A249920 #10 Mar 22 2022 00:11:17 %S A249920 1,5,2,4,3,6,8,7,9,11,10,12,13,14,17,15,16,18,20,19,21,23,22,24,25,26, %T A249920 28,27,29,32,30,31,33,35,34,36,38,37,39,41,40,42,43,44,46,45,47,48,50, %U A249920 49,51,53,52,54,56,55,57,58,59,60,61,62,63,65,64,66,67 %N A249920 Inverse permutation to A055266. %H A249920 Reinhard Zumkeller, <a href="/A249920/b249920.txt">Table of n, a(n) for n = 1..10000</a> %H A249920 <a href="/index/Per#IntegerPermutation">Index entries for sequences that are permutations of the natural numbers</a> %o A249920 (Haskell) %o A249920 import Data.List (elemIndex); import Data.Maybe (fromJust) %o A249920 a249920 = (+ 1) . fromJust . (`elemIndex` a055266_list) %Y A249920 Cf. A055266, A249918. %K A249920 nonn %O A249920 1,2 %A A249920 _Reinhard Zumkeller_, Jan 14 2015