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 A115598 #30 Sep 20 2017 02:51:49
%S A115598 1,8,49,288,1681,9800,57121,332928,1940449,11309768,65918161,
%T A115598 384199200,2239277041,13051463048,76069501249,443365544448,
%U A115598 2584123765441,15061377048200,87784138523761,511643454094368,2982076586042449,17380816062160328,101302819786919521
%N A115598 Consider all Pythagorean triples (X,X+1,Z) ordered by increasing Z; sequence gives Z-(X+1) values.
%C A115598 Old name was A001653(n) - A046090(n).
%H A115598 Vincenzo Librandi, <a href="/A115598/b115598.txt">Table of n, a(n) for n = 1..200</a>
%H A115598 L. J. Gerstein, <a href="http://www.jstor.org/stable/30044157">Pythagorean triples and inner products</a>, Math. Mag., 78 (2005), 205-213.
%H A115598 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (7,-7,1).
%F A115598 a(n) = (-2+(3-2*sqrt(2))^n+(3+2*sqrt(2))^n)/4.
%F A115598 a(n) = 7*a(n-1)-7*a(n-2)+a(n-3).
%F A115598 G.f.: -x*(x+1) / ((x-1)*(x^2-6*x+1)).
%F A115598 a(n)^2 + (a(n)+1)^2 = A001542(n)^2 + 1^2. - _Hermann Stamm-Wilbrandt_, Jul 27 2014
%t A115598 LinearRecurrence[{7,-7,1},{1,8,49},30] (* _Harvey P. Dale_, Oct 27 2013 *)
%t A115598 CoefficientList[Series[-(x + 1)/((x - 1) (x^2 - 6 x + 1)), {x, 0, 30}], x] (* _Vincenzo Librandi_, Jul 28 2014 *)
%Y A115598 Essentially a duplicate of A001108.
%K A115598 nonn,easy
%O A115598 1,2
%A A115598 _N. J. A. Sloane_, Mar 14 2006
%E A115598 Corrected and edited by _Colin Barker_, Jul 31 2013