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 A098961 #17 Sep 02 2025 21:56:28
%S A098961 13,26,52,65,104,117,130,169,208,221,234,260,325,338,377,416,442,468,
%T A098961 481,520,533,585,637,650,676,689,754,793,832,845,884,936,949,962,1040,
%U A098961 1053,1066,1105,1157,1170,1261,1274,1300,1313
%N A098961 Sums of two squares and divisible by 13.
%H A098961 Robert Israel, <a href="/A098961/b098961.txt">Table of n, a(n) for n = 1..10000</a>
%F A098961 a(n) = 13 * A001481(n+1) for n >= 1. - _Joerg Arndt_, Dec 03 2022
%e A098961 Sums not divisible by 13 are shown in asterisks:
%e A098961 .
%e A098961 | 1 4 9 16 25 36 49 64 81 100 121
%e A098961 ----+------------------------------------------------------
%e A098961 1 | * * * * 26 * * 65 * * *
%e A098961 4 | * * 13 * * * * * * 104 *
%e A098961 9 | * 13 * * * * * * * * 130
%e A098961 16 | * * * * * 52 65 * * * *
%e A098961 25 | 26 * * * * * * * * * *
%e A098961 36 | * * * 52 * * * * 117 * *
%e A098961 49 | * * * 65 * * * * 130 * *
%e A098961 64 | 65 * * * * * * * * * *
%e A098961 81 | * * * * * 117 130 * * * *
%e A098961 100 | * 104 * * * * * * * * 221
%e A098961 121 | * * 130 * * * * * * 221 *
%p A098961 filter:= proc(n) local t,F;
%p A098961 F:= select(t -> t[2]::odd, ifactors(n)[2]);
%p A098961 andmap(t -> t[1] = 2 or t[1] mod 4 = 1, F);
%p A098961 end proc:
%p A098961 select(filter, [seq(i,i=13..10000, 13)]); # _Robert Israel_, Dec 02 2022
%t A098961 With[{nn=50},Take[Union[Select[Total/@Subsets[Range[nn]^2,{2}], Divisible[ #,13]&]],nn]] (* _Harvey P. Dale_, Aug 15 2014 *)
%Y A098961 Intersection of A001481 and A008595.
%Y A098961 Cf. A094447.
%K A098961 nonn,changed
%O A098961 1,1
%A A098961 Jun Mizuki (suzuki32(AT)sanken.osaka-u.ac.jp), Oct 22 2004