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 A281647 #12 Jan 26 2017 12:41:54
%S A281647 2,22,98,838,3722,31822,141338,1208398,5367122,45887302,203809298,
%T A281647 1742509078,7739386202,66169457662,293892866378,2512696882078,
%U A281647 11160189536162,95416312061302,423793309507778,3623307161447398,16092985571759402,137590255822939822
%N A281647 Solutions x to the negative Pell equation x^2 - 10*y^2 = -6 with x > y > 0.
%C A281647 The corresponding values of y are in A221875.
%H A281647 Colin Barker, <a href="/A281647/b281647.txt">Table of n, a(n) for n = 1..1000</a>
%H A281647 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (0,38,0,-1).
%F A281647 G.f.: 2*x*(1 + x)*(1 + 10*x + x^2) / ((1 + 6*x - x^2)*(1 - 6*x - x^2)).
%F A281647 a(n) = 38*a(n-2) - a(n-4) for n>4.
%F A281647 a(n) = ((3-r)^n + (-3-r)^n*(-3+r) - 3*(-3+r)^n - r*(-3+r)^n + (3+r)^n)/2, where r=sqrt(10).
%e A281647 22 is in the sequence because (x, y) = (22, 7) is a solution to x^2 - 10*y^2 = -6.
%t A281647 CoefficientList[ Series[(2 (1 + 11x + 11x^2 + x^3))/(1 - 38x^2 + x^4), {x, 0, 21}], x] (* or *)
%t A281647 LinearRecurrence[{0, 38, 0, -1}, {2, 22, 98, 838}, 22] (* _Robert G. Wilson v_, Jan 26 2017 *)
%o A281647 (PARI) Vec(2*x*(1 + x)*(1 + 10*x + x^2) / ((1 + 6*x - x^2)*(1 - 6*x - x^2)) + O(x^30))
%Y A281647 Cf. A221875.
%K A281647 nonn,easy
%O A281647 1,1
%A A281647 _Colin Barker_, Jan 26 2017