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 A214421 #8 Jul 06 2018 09:47:27
%S A214421 4,5,6,7,8,9,10,11,15,16,17,18,19,20,21,22,23,26,27,28,29,30,31,32,37,
%T A214421 38,39,40,41,42,43,44,47,48,49,50,51,52,53,54,55,56,58,59,60,61,62,63,
%U A214421 68,69,70,71,72,73,74,75,79,80,81,82,83,84,85,86,87,89
%N A214421 Numbers not representable as the sum of three 12-gonal numbers.
%C A214421 There are an infinite number of numbers that are not the sum of three 12-gonal numbers.
%D A214421 R. K. Guy, Unsolved Problems in Number Theory, D3.
%H A214421 T. D. Noe, <a href="/A214421/b214421.txt">Table of n, a(n) for n = 1..10000</a>
%H A214421 R. K. Guy, <a href="https://www.jstor.org/stable/2324367">Every number is expressible as the sum of how many polygonal numbers?</a>, Amer. Math. Monthly 101 (1994), 169-172.
%t A214421 nn = 100; dod = Table[n*(5n-4), {n, 0, nn}]; t = Table[0, {dod[[-1]]}]; Do[n = dod[[i]] + dod[[j]] + dod[[k]]; If[n <= dod[[-1]], t[[n]] = 1], {i, nn}, {j, i, nn}, {k, j, nn}]; Flatten[Position[t, 0]]
%Y A214421 Cf. A051624 (12-gonal numbers).
%Y A214421 Cf. A118278, A118279.
%K A214421 nonn
%O A214421 1,1
%A A214421 _T. D. Noe_, Jul 17 2012