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 A077237 #12 Feb 12 2017 02:12:20
%S A077237 1,2,6,9,23,34,86,127,321,474,1198,1769,4471,6602,16686,24639,62273,
%T A077237 91954,232406,343177,867351,1280754,3236998,4779839,12080641,17838602,
%U A077237 45085566,66574569,168261623
%N A077237 Combined Diophantine Chebyshev sequences A054491 and A077234.
%C A077237 -3*a(n)^2 + b(n)^2 = 13, with the companion sequence b(n)= A077238(n).
%H A077237 Matthew House, <a href="/A077237/b077237.txt">Table of n, a(n) for n = 0..3478</a>
%H A077237 <a href="/index/Ch#Cheby">Index entries for sequences related to Chebyshev polynomials.</a>
%H A077237 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (0,4,0,-1).
%F A077237 a(2*k)= A054491(k) and a(2*k+1)= A077234(k), k>=0.
%F A077237 G.f.: (1+x)*(1+x+x^2)/(1-4*x^2+x^4).
%F A077237 a(n) = 4*a(n-2) - a(n-4). - _Matthew House_, Feb 11 2017
%e A077237 3*a(2)^2 + 13 = 3*36+13 = 121 = 11^2 = A077238(2)^2.
%t A077237 CoefficientList[Series[(1 + x) (1 + x + x^2)/(1 - 4 x^2 + x^4), {x, 0, 28}], x] (* _Michael De Vlieger_, Feb 11 2017 *)
%K A077237 nonn,easy
%O A077237 0,2
%A A077237 _Wolfdieter Lang_, Nov 08 2002