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 A189356 #34 Sep 08 2022 08:45:56
%S A189356 3,41,571,7953,110771,1542841,21489003,299303201,4168755811,
%T A189356 58063278153,808717138331,11263976658481,156886956080403,
%U A189356 2185153408467161,30435260762459851,423908497265970753,5904283700961130691,82236063316189858921,1145400602725696894203
%N A189356 a(n) gives y-values solving the Diophantine equation 2*x^2 + (x-1)^2 = y^2 for positive x.
%C A189356 (a(n)-1)/2 gives indices of triangular numbers which are also pentagonal (A046175).
%H A189356 Vincenzo Librandi, <a href="/A189356/b189356.txt">Table of n, a(n) for n = 1..200</a>
%H A189356 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (14,-1).
%F A189356 a(n) = 14*a(n-1) - a(n-2).
%F A189356 G.f.: x*(3-x)/(1-14*x+x^2). - _Bruno Berselli_, May 03 2011
%t A189356 LinearRecurrence[{14,-1}, {3, 41}, 19] (* _Bruno Berselli_, Nov 11 2011 *)
%o A189356 (Magma) [n le 2 select 38*n-35 else 14*Self(n-1)-Self(n-2): n in [1..19]]; // _Bruno Berselli_, May 03 2011
%Y A189356 Cf. A081065, A046174, A046175.
%K A189356 nonn
%O A189356 1,1
%A A189356 _Sture Sjöstedt_, May 02 2011
%E A189356 Extended by _T. D. Noe_, May 02 2011