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 A174428 #12 Aug 04 2025 11:35:46
%S A174428 0,0,1,0,0,1,0,1,1,3,0,0,0,2,1,0,0,0,0,2,0,0,0,2,0,3,2,1,0,1,0,3,0,3,
%T A174428 1,7,0,1,1,1,3,1,6,5,4,0,0,0,2,3,0,4,2,0,8,0,0,0,0,2,0,5,4,3,2,1,0,0,
%U A174428 1,0,3,4,0,4,1,8,6,4,0,0,2,2,4,2,0,6,5,4,3,2,1,0,0,0,0,4,0,3,0,6,4,2,0,11,10
%N A174428 Triangle read by rows: R(n,k) = sigma(n) mod k, where sigma(.) is the sum of divisors.
%e A174428 The triangle starts in row n=1 with columns 1<=k<=n as:
%e A174428 0;
%e A174428 0,1;
%e A174428 0,0,1;
%e A174428 0,1,1,3;
%e A174428 0,0,0,2,1;
%e A174428 0,0,0,0,2,0;
%e A174428 0,0,2,0,3,2,1;
%t A174428 Flatten[Table[Mod[DivisorSigma[1,n],k],{n,20},{k,n}]] (* _Harvey P. Dale_, Apr 17 2014 *)
%Y A174428 Cf. A000203, A154234.
%K A174428 nonn,tabl
%O A174428 1,10
%A A174428 _Juri-Stepan Gerasimov_, Nov 28 2010