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 A103819 #20 Nov 02 2024 17:30:22
%S A103819 0,1,3,8,23,63,172,471,1287,3516,9607,26247,71708,195911,535239,
%T A103819 1462300,3995079,10914759,29819676,81468871,222577095,608091932,
%U A103819 1661338055,4538859975,12400396060,33878512071,92557816263,252872656668
%N A103819 Whitney transform of Jacobsthal numbers.
%C A103819 The Whitney transform maps the sequence with g.f. g(x) to that with g.f. (1/(1-x))*g(x(1+x)).
%H A103819 Harvey P. Dale, <a href="/A103819/b103819.txt">Table of n, a(n) for n = 0..1000</a>
%H A103819 <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (2,2,1,-2,-2).
%F A103819 G.f.: x(1+x)/((1-x)(1+x+x^2)(1-2x-2x^2)).
%F A103819 a(n) = 2a(n-1)+2a(n-2)+a(n-3)-2a(n-4)-2a(n-5).
%F A103819 a(n) = Sum_{k=0..n} Sum_{i=0..n} C(k, i-k)*A001045(k).
%F A103819 9*a(n) = -2 +2*(A002605(n)+2*A002605(n+1))-A099837(n+3). - _R. J. Mathar_, Oct 23 2011
%t A103819 LinearRecurrence[{2,2,1,-2,-2},{0,1,3,8,23},30] (* _Harvey P. Dale_, Nov 02 2024 *)
%Y A103819 Cf. A004070, A001045, A002605, A099837.
%K A103819 easy,nonn
%O A103819 0,3
%A A103819 _Paul Barry_, Feb 16 2005