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 A337658 #9 Oct 02 2020 02:30:24
%S A337658 1,5,11,13,15,18,19,21,25,26,28,31,34,35,39,40,41,42,43,45,47,48,49,
%T A337658 50,54,56,58,59,60,61,63,64,66,67,68,71,74,76,77,78,79,80,82,84,85,86,
%U A337658 87,88,89,93,94,96,98,101,104,107,109,110,111,113,114,115,117,119,120,122,124,127
%N A337658 Let M_k denote the addition table for the first k terms of A337655. M_k contains exactly k*(k+1)/2 distinct numbers, and these numbers are a subset of the entries in M_{k+1}. The present sequence consists of the numbers that never appear in any M_k.
%H A337658 Rémy Sigrist, <a href="/A337658/b337658.txt">Table of n, a(n) for n = 1..10000</a>
%H A337658 Rémy Sigrist, <a href="/A337658/a337658.txt">C++ program for A337658</a>
%o A337658 (C++) See Links section.
%Y A337658 Cf. A337655, A337656, A337657.
%K A337658 nonn
%O A337658 1,2
%A A337658 _Jean-Paul Delahaye_, Oct 01 2020