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 A088920 #11 Feb 16 2025 08:32:51
%S A088920 2,50,1682,57122,1940450,65918162,2239277042,76069501250,
%T A088920 2584123765442,87784138523762,2982076586042450,101302819786919522,
%U A088920 3441313796169221282,116903366249966604050,3971273138702695316402
%N A088920 Solutions k to the Diophantine equation k = 2n^2 = m^2+1.
%H A088920 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/NSWNumber.html">NSW Number</a>
%H A088920 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (35, -35, 1).
%F A088920 G.f.: (2x^2 - 20x + 2)/((1-x)(1 - 34x + x^2)).
%F A088920 a(n) = -(sinh((2n - 1) arctanh(sqrt(2))))^2 = 1 -(cosh((2n - 1) arctanh(sqrt(2))))^2. - _Artur Jasinski_, Oct 30 2008
%t A088920 Table[Round[N[ -(Sinh[(2 n - 1) ArcTanh[Sqrt[2]]])^2, 100]], {n, 1, 20}] (* _Artur Jasinski_, Oct 30 2008 *)
%Y A088920 Corresponding solutions of n are A001653 and m are A002315.
%Y A088920 A008843(n-1) + 1.
%K A088920 nonn
%O A088920 1,1
%A A088920 _Eric W. Weisstein_, Oct 23 2003