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 A075405 #16 Apr 16 2025 05:35:36
%S A075405 70,0,5,0,0,0,92,0,106,0,2001863,0,652,0,679,0,138,77,0,29,724,413,0,
%T A075405 0,182,0,253,385,0,1612,0,8687,0,0,0,0,0,143,0,0,0,0,0,274,0,0,0,0,0,
%U A075405 1281,0,1012,0,0,121268,0,0,56855,0,440,0,0,0,3069,2725,0,655,0,0,0,0,0,1525,4035066,0,430,0,0,0,0,0,0,2619,0,0,0,795,0,0,0,3465,0,0,0,0,0,0,0,0,0
%N A075405 a(n)^2 is the square obtained in A075404 (or 0 if no such square exists).
%D A075405 See A180244.
%e A075405 a(1) = 70 because 1^2+...+24^2 = a(1)^2 = 70^2.
%t A075405 s[n_, k_]:=Module[{m=n+k-1}, (m(m+1)(2m+1)-n(n-1)(2n-1))/6]; mx=40000; Table[k=2; While[k<mx && !IntegerQ[Sqrt[s[n, k]]], k++]; If[k==mx, 0, Sqrt[s[n, k]]], {n, 100}]
%Y A075405 Cf. A000330, A075404, A075406.
%K A075405 nonn
%O A075405 1,1
%A A075405 _Zak Seidov_, Sep 13 2002
%E A075405 Corrected and extended by _Lior Manor_, Sep 19 2002
%E A075405 Corrected and edited by _T. D. Noe_, Jan 21 2011