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 A099520 #4 Jun 29 2013 06:22:06 %S A099520 1,2,4,5,3,7,11,10,6,12,8,14,22,17,25,20,28,23,13,44,16,26,18,51,21, %T A099520 29,49,32,24,34,56,37,27,39,63,42,30,81,33,45,35,47,79,50,38,52,40,54, %U A099520 90,57,43,59,97,9,99,66,46,68,48,70,110,73,113,76,116,144,120,148,124,83 %N A099520 a(1)=1; for n>1, a(n)=smallest integer m>0 not yet appearing in sequence such that m+a(n-1) is a multiple of n-1. %e A099520 a(1)=1. a(2)=2 because a(2)+a(1)=2+1=3 which is a multiple of 1. Could not use a(2)=1 since 1 has already been used. a(3)=4 so that a(3)+a(2)=4+2=6 which is a multiple of 2, etc. %Y A099520 Cf. A099506 for similar sequence with a(n)+a(n-1)=multiple of n. %K A099520 easy,nonn %O A099520 1,2 %A A099520 Mark Hudson (mrmarkhudson(AT)hotmail.com), Oct 20 2004