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 A026950 #18 Dec 27 2024 14:55:40
%S A026950 1,3,10,25,75,175,500,1125,3125,6875,18750,40625,109375,234375,625000,
%T A026950 1328125,3515625,7421875,19531250,41015625,107421875,224609375,
%U A026950 585937500,1220703125,3173828125,6591796875,17089843750,35400390625,91552734375,189208984375,488281250000
%N A026950 a(n) = Sum_{k=0..n} (k+1) * T(n,k), with T given by A026374.
%H A026950 Andrew Howroyd, <a href="/A026950/b026950.txt">Table of n, a(n) for n = 0..1000</a>
%H A026950 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (0,10,0,-25).
%F A026950 a(n) = (n + 2) * (7 + 3*(-1)^n) * 5^floor((n-1)/2) / 4.
%F A026950 From _Colin Barker_, Oct 13 2012: (Start)
%F A026950 a(n) = 10*a(n-2) - 25*a(n-4).
%F A026950 G.f.: -(5*x^3-3*x-1)/(5*x^2-1)^2. (End)
%o A026950 (PARI) a(n) = (n + 2) * (7 + 3*(-1)^n) * 5^((n-1)\2) / 4 \\ _Andrew Howroyd_, Dec 27 2024
%Y A026950 Cf. A026374.
%K A026950 nonn,easy
%O A026950 0,2
%A A026950 _Clark Kimberling_
%E A026950 a(28) onwards from _Andrew Howroyd_, Dec 27 2024