cp's OEIS Frontend

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.

A234004 Smallest number which is the sum of two positive triangular numbers (A000217) in at least n ways.

This page as a plain text file.
%I A234004 #19 Apr 28 2020 11:57:05
%S A234004 2,16,81,471,1056,1381,6906,6906,17956,34531,40056,40056,200281,
%T A234004 200281,200281,200281,520731,520731,1001406,1001406,1482081,1482081,
%U A234004 1482081,1482081,7410406,7410406,7410406,7410406,7410406,7410406,7410406,7410406
%N A234004 Smallest number which is the sum of two positive triangular numbers (A000217) in at least n ways.
%H A234004 Donovan Johnson, <a href="/A234004/b234004.txt">Table of n, a(n) for n = 1..216</a>
%e A234004 2 = 1+1; 16 = 1+15 = 6+10; 81 = 3+78 = 15+66 = 36+45.
%t A234004 poly[n_,k_]:=n (n-1)(k-2)/2+n;nn=10^5;order=3;t2=Table[0,{nn}];n2=Floor[(-4+#+Sqrt[(-4+#)^2+8 (-2+#) nn])/(2 (-2+#))&[order]];Do[r=Plus@@poly[{a,b},order];If[r<=nn,t2[[r]]++],{a,n2},{b,a,n2}];t={};n=1;While[a=Position[t2,_?(#>=n&),1,1];a!={},AppendTo[t,a[[1,1]]];n++];t (* after _T. D. Noe_ (A048610) *)
%Y A234004 Cf. A000217, A048610, A199809, A052346, A053587.
%K A234004 nonn
%O A234004 1,1
%A A234004 _Vladimir Shevelev_ and _Peter J. C. Moses_, Dec 18 2013