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 A269451 #19 Oct 22 2016 10:37:33
%S A269451 7,28,44,67,87,124,168,287,379,512,628,843,1099,1792,2328,3103,3779,
%T A269451 5032,6524,10563,13687,18204,22144,29447,38143,61684,79892,106219,
%U A269451 129183,171748,222432,359639,465763,619208,753052,1001139,1296547,2096248,2714784
%N A269451 The first of 50 consecutive positive integers the sum of the squares of which is a square.
%C A269451 Positive integers y in the solutions to 2*x^2-100*y^2-4900*y-80850 = 0.
%C A269451 Numbers n such that 40425 + 2450*n + 50*n^2 is a square. - _Harvey P. Dale_, Oct 22 2016
%H A269451 Colin Barker, <a href="/A269451/b269451.txt">Table of n, a(n) for n = 1..1000</a>
%H A269451 <a href="/index/Rec#order_13">Index entries for linear recurrences with constant coefficients</a>, signature (1,0,0,0,0,6,-6,0,0,0,0,-1,1).
%F A269451 G.f.: x*(7+21*x+16*x^2+23*x^3+20*x^4+37*x^5+2*x^6-7*x^7-4*x^8-5*x^9-4*x^10-7*x^11-x^12) / ((1-x)*(1+2*x^3-x^6)*(1-2*x^3-x^6)).
%e A269451 7 is in the sequence because sum(k=7, 56, k^2) = 60025 = 245^2.
%t A269451 Select[Range[3*10^6],IntegerQ[Sqrt[40425+2450#+50#^2]]&] (* or *) LinearRecurrence[ {1,0,0,0,0,6,-6,0,0,0,0,-1,1},{7,28,44,67,87,124,168,287,379,512,628,843,1099},40] (* _Harvey P. Dale_, Oct 22 2016 *)
%o A269451 (PARI) Vec(x*(7+21*x+16*x^2+23*x^3+20*x^4+37*x^5+2*x^6-7*x^7-4*x^8-5*x^9-4*x^10-7*x^11-x^12) / ((1-x)*(1+2*x^3-x^6)*(1-2*x^3-x^6)) + O(x^40))
%Y A269451 Cf. A001032, A001652, A094196, A106521, A257781, A269447, A269448, A269449.
%K A269451 nonn,easy,less
%O A269451 1,1
%A A269451 _Colin Barker_, Feb 27 2016