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 A214419 #17 Jul 09 2018 23:23:24
%S A214419 4,5,6,7,8,9,13,14,15,16,17,18,19,22,23,24,25,26,31,32,33,34,35,36,39,
%T A214419 40,41,42,43,44,45,46,48,49,50,51,56,57,58,59,60,61,65,66,67,68,69,70,
%U A214419 71,73,74,75,76,77,78,82,83,84,88,90,91,92,93,94,97,98
%N A214419 Numbers not representable as the sum of three 10-gonal numbers.
%C A214419 It is conjectured that 7687 positive numbers are not the sum of three 10-gonal numbers.
%D A214419 R. K. Guy, Unsolved Problems in Number Theory, D3.
%H A214419 T. D. Noe, <a href="/A214419/b214419.txt">Table of n, a(n) for n = 1..7687</a>
%H A214419 R. K. Guy, <a href="https://doi.org/10.1080/00029890.1994.11996925">Every number is expressible as the sum of how many polygonal numbers?</a>, Amer. Math. Monthly 101 (1994), 169-172.
%H A214419 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 A214419 nn = 750; dec = Table[n*(4*n-3), {n, 0, nn}]; t = Table[0, {dec[[-1]]}]; Do[n = dec[[i]] + dec[[j]] + dec[[k]]; If[n <= dec[[-1]], t[[n]] = 1], {i, nn}, {j, i, nn}, {k, j, nn}]; Flatten[Position[t, 0]]
%Y A214419 Cf. A001107 (10-gonal numbers).
%Y A214419 Cf. A118278, A118279.
%K A214419 nonn,fini
%O A214419 1,1
%A A214419 _T. D. Noe_, Jul 17 2012