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 A203924 #19 Dec 23 2024 14:53:43 %S A203924 372,441,483,492,651,672,861,2412,2532,2652,3162,3472,3612,3720,3732, %T A203924 3782,3852,3913,3972,4053,4182,4221,4263,4410,4431,4473,4592,4623, %U A203924 4641,4683,4704,4812,4824,4830,4851,4853,4893,4920,4932,4944,6132,6174,6231,6293 %N A203924 Indices of terms which appear at least twice already earlier in A061205. %C A203924 Motivated by a question from Franklin T. Adams-Watters, cf. link. %H A203924 M. F. Hasler, <a href="/A203924/b203924.txt">Table of n, a(n) for n = 1..101</a> %H A203924 Franklin T. Adams-Watters, <a href="https://web.archive.org/web/*/http://list.seqfan.eu/oldermail/seqfan/2012-January/008842.html">Number times reversal</a>, SeqFan list, Jan 07 2012 %H A203924 Hans Havermann, <a href="http://chesswanks.com/seq/b203924.html">Augmented table of n, a(n) (in bold) and its associated indices, for n = 1..21313</a> %e A203924 A061205(156)=101556=A061205(273)=A061205(372), and this is the first time a term appears for the third time in A061205, therefore a(1)=372. %o A203924 (PARI) seen=dupe=[];for(n=0,999999, setsearch(seen,t=A061205(n)) | !(seen=setunion(seen,Set(t))) | next; setsearch(dupe,t) & (print1(n",")|next); dupe=setunion(dupe,Set(t))) %K A203924 nonn,base %O A203924 1,1 %A A203924 _M. F. Hasler_, Jan 07 2012 %E A203924 a(8)-a(44) from _Donovan Johnson_, Jan 07 2012