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 A108742 #26 May 31 2019 05:12:07
%S A108742 1,2,3,7,12,24,45,86,164,312,595,1133,2159,4113,7836,14929,28442,
%T A108742 54187,103235,196680,374708,713881,1360062,2591144,4936560,9404967,
%U A108742 17918025,34136815,65036305,123904968,236059553,449732674,856815475,1632375855
%N A108742 Row sums of a triangle related to the Jacobsthal polynomials.
%C A108742 Row sums of A108756.
%H A108742 Harvey P. Dale, <a href="/A108742/b108742.txt">Table of n, a(n) for n = 0..1000</a>
%H A108742 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (1,2,0,-1).
%F A108742 G.f.: (1 + x - x^2)/(1 - x - 2*x^2 + x^4).
%F A108742 a(n) = a(n - 1) + 2*a(n - 2) - a(n - 4) for n >= 4.
%F A108742 a(n) = Sum_{0 <= k <= n} binomial(floor((n + k + 1)/2) + k, floor((n + k)/2) - k).
%t A108742 LinearRecurrence[{1,2,0,-1},{1,2,3,7},40] (* _Harvey P. Dale_, Feb 21 2016 *)
%K A108742 easy,nonn
%O A108742 0,2
%A A108742 _Paul Barry_, Jun 22 2005