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 A026842 #15 Jul 22 2025 13:38:30
%S A026842 1,9,56,300,1487,7041,32381,146017,649395,2859231,12494914,54291912,
%T A026842 234860677,1012433965,4352210327,18666918033,79916230409,341615895659,
%U A026842 1458457275715,6220016154525,26503542364381,112847001503099,480173686483581
%N A026842 a(n) = T(2n,n-3), T given by A026725.
%C A026842 Column k=8 of triangle A236830. - _Philippe Deléham_, Feb 02 2014
%H A026842 G. C. Greubel, <a href="/A026842/b026842.txt">Table of n, a(n) for n = 3..1000</a>
%F A026842 a(n) = A026846(n) = A026849(n). - _Philippe Deléham_, Feb 02 2014
%F A026842 G.f.: (x^3*C(x)^8)/(1-x*C(x)^3) where C(x) is the g.f. of A000108. - _Philippe Deléham_, Feb 02 2014
%F A026842 D-finite with recurrence -(n+3)*(253*n-940)*a(n) +(3061*n^2-6571*n-18156)*a(n-1) +(-12091*n^2+43849*n-996)*a(n-2) +(14543*n^2-76721*n+109596)*a(n-3) +2*(1037*n-2568)*(2*n-5)*a(n-4)=0. - _R. J. Mathar_, Jul 22 2025
%t A026842 Drop[CoefficientList[Series[(1-Sqrt[1-4*x])^8/(32*x^3*(8*x^2 -(1 - Sqrt[1-4*x])^3 )), {x,0,30}], x],3] (* _G. C. Greubel_, Jul 17 2019 *)
%o A026842 (PARI) my(x='x+O('x^30)); Vec((1-sqrt(1-4*x))^8/(32*x^3*(8*x^2 -(1 - sqrt(1-4*x))^3 ))) \\ _G. C. Greubel_, Jul 17 2019
%o A026842 (Magma) R<x>:=PowerSeriesRing(Rationals(), 30); Coefficients(R!( (1-Sqrt(1-4*x))^8/(32*x^3*(8*x^2 -(1-Sqrt(1-4*x))^3 )) )); // _G. C. Greubel_, Jul 17 2019
%o A026842 (Sage) a=((1-sqrt(1-4*x))^8/(32*x^3*(8*x^2 -(1-sqrt(1-4*x))^3 ))).series(x, 30).coefficients(x, sparse=False); a[3:] # _G. C. Greubel_, Jul 17 2019
%Y A026842 Cf. A236830, A026846, A026849.
%K A026842 nonn
%O A026842 3,2
%A A026842 _Clark Kimberling_