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 A215069 #12 Jul 22 2025 23:20:49 %S A215069 2,4,5,7,8,9,10,11,13,14,16,17,19,20,22,23,24,25,26,27,28,29,30,31,32, %T A215069 34,35,37,38,39,40,41,42,43,44,45,46,47,49,50,52,53,54,55,56,57,58,59, %U A215069 60,61,62,63,64,65,67,68,69,70,71,72,73,74,75,76,77,79,80,82,83,84,85 %N A215069 Natural numbers that when squared can be expressed as sums of a positive square number and a positive triangular number. %C A215069 There are infinitely many terms (see A214937 for a proof) %H A215069 Ivan N. Ianakiev, <a href="/A215069/b215069.txt">Table of n, a(n) for n = 1..1000</a> %F A215069 a(n) = sqrt(A214937(n)) %e A215069 2 and 7 are in the sequence because 2^2=1^2+2*3/2 and 7^2=2^2+9*10/2 %Y A215069 Cf. A000217, A000290, A214937 %K A215069 nonn %O A215069 1,1 %A A215069 _Ivan N. Ianakiev_, Aug 02 2012