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 A108920 #3 Mar 30 2012 17:37:53 %S A108920 0,1,2,2,2,4,2,3,4,5,2,7,2,5,7,4,2,8,2,7,8,5,2,10,4,5,6,7,2,15,2,5,8, %T A108920 5,7,13,2,5,8,10,2,15,2,8,12,5,2,13,4,9,8,8,2,12,8,10,8,5,2,23,2,5,13, %U A108920 6,8,15,2,8,8,16,2,17,2,5,13,8,7,16,2,13,8,5,2,23,8,5,8,10,2,26,7,8,8,5,8 %N A108920 Number of positive integers k>n such that n+k divides n^2+k^2. %C A108920 If n+k divides n^2+k^2 then k<=n(2n+1). If n>2 then there are at least two values of k>n such that n+k divides n^2+k^2; they are k=n(n-1) and k=n(2n-1). Further, if n is prime, these are the only two values. If n=2^j, then there are exactly j values of k>x such that n+k divides n^2+k^2; they are k=3n, k=7n, k=15n,..., k=(2x-1)n. Is this sequence the same as A066761 except for the prepended a(1)=0? %e A108920 6+k divides 36+k^2 only for k=12,18,30 and 66, so a(6)=4. %Y A108920 Cf. A066761. %K A108920 nonn %O A108920 1,3 %A A108920 _John W. Layman_, Jul 19 2005