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 A340272 #18 Jan 21 2021 22:22:09 %S A340272 0,1,3,5,2,7,4,17,9,14,6,19,11,24,16,29,8,21,13,65,26,83,18,31,10,62, %T A340272 23,93,15,54,28,98,85,59,20,33,12,77,64,196,25,95,82,214,56,43,30,100, %U A340272 87,219,61,48,22,35,92,480,79,211,53,198,27,185,97,891,84,216,58 %N A340272 First position of n in A308712, or -1 if that number is not in A308712. %H A340272 Rémy Sigrist, <a href="/A340272/b340272.txt">Table of n, a(n) for n = 0..10000</a> %H A340272 Rémy Sigrist, <a href="/A340272/a340272.gp.txt">PARI program for A340272</a> %e A340272 A308712(2)=4, so a(4)=2. %o A340272 (PARI) See Links section. %Y A340272 Cf. A308712. %K A340272 nonn %O A340272 0,3 %A A340272 _J. Lowell_, Jan 02 2021 %E A340272 a(0) = 0 added and escape clause adjusted by _Rémy Sigrist_, Jan 17 2021