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 A361491 #15 Jun 10 2024 08:53:11
%S A361491 1,73,2521,85681,2910673,98877241,3358915561,114104251873,
%T A361491 3876185648161,131676207785641,4473114879063673,151954229680379281,
%U A361491 5161970694253831921,175355049374949906073,5956909708054042974601,202359575024462511230401,6874268641123671338859073,233522774223180363009978121
%N A361491 Expansion of x*(1+38*x+x^2)/((1-x)*(x^2-34*x+1)).
%C A361491 Indices i of Tetrahedral Numbers T(i) such that T(i)*T(2*i) is a perfect square. [Ulas]
%H A361491 Paolo Xausa, <a href="/A361491/b361491.txt">Table of n, a(n) for n = 1..500</a>
%H A361491 Maciej Ulas, <a href="https://arxiv.org/abs/0811.2477">On certain diophantine equations related to triangular and tetrahedral numbers</a>, arXiv:0811.2477 [math.NT] (2008) , u_n in Theorem 5.6.
%H A361491 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (35,-35,1).
%F A361491 a(n) = 35*a(n-1) -35*a(n-2) +a(n-3).
%F A361491 a(n) = 17*a(n-1)+36*A046176(n-1)+20. [Ulas]
%F A361491 4*a(n) = -5+9*(A029547(n)-33*A029547(n-1)).
%t A361491 LinearRecurrence[{35, -35, 1}, {1, 73, 2521}, 20] (* _Paolo Xausa_, Jan 18 2024 *)
%Y A361491 Cf. A046176.
%K A361491 nonn,easy
%O A361491 1,2
%A A361491 _R. J. Mathar_, Mar 14 2023