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 A371221 #6 Mar 16 2024 15:20:34 %S A371221 1,3,2,5,7,9,11,13,15,4,17,19,21,23,25,27,29,31,33,35,37,39,41,43,45, %T A371221 47,49,51,53,55,57,59,61,63,65,67,69,71,73,75,77,79,8,81,83,85,87,89, %U A371221 91,93,95,6,97,10,99,101,103,105,107,109,111,113,115,117,12 %N A371221 Inverse permutation to A371220. %H A371221 Rémy Sigrist, <a href="/A371221/a371221.gp.txt">PARI program</a> %H A371221 <a href="/index/Per#IntegerPermutation">Index entries for sequences that are permutations of the natural numbers</a> %F A371221 a(n) <= 2*n. %e A371221 A371220(42) = 231, so a(231) = 42. %o A371221 (PARI) See Links section. %Y A371221 Cf. A371220. %K A371221 nonn %O A371221 1,2 %A A371221 _Rémy Sigrist_, Mar 15 2024