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 A230414 #9 Nov 08 2013 13:46:48 %S A230414 0,1,2,0,0,3,4,5,0,0,6,7,8,0,0,9,10,11,0,0,0,0,0,12,13,14,0,0,15,16, %T A230414 17,0,0,18,19,20,0,0,21,22,23,0,0,0,0,0,24,25,26,0,0,27,28,29,0,0,30, %U A230414 31,32,0,0,33,34,35,0,0,0,0,0,36,37,38,0,0,39,40,41 %N A230414 Inverse function for injection A219650. %C A230414 a(0)=0; thereafter if n occurs as a term of A219650, a(n)=its position in A219650, otherwise zero. This works as an "inverse" function for A219650 in a sense that a(A219650(n)) = n for all n. %H A230414 Antti Karttunen, <a href="/A230414/b230414.txt">Table of n, a(n) for n = 0..10079</a> %F A230414 a(n) = A230412(n) * A230413(n). %F A230414 a(n) = A230423(n)/2. %o A230414 (Scheme) %o A230414 (define (A230414 n) (* (A230412 n) (A230413 n))) %Y A230414 Cf. A219650, A230423, A230424. A219658 gives the positions of zeros after the first one. Analogous sequence for binary system: A213714. %K A230414 nonn %O A230414 0,3 %A A230414 _Antti Karttunen_, Oct 31 2013