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 A103771 #15 May 07 2025 09:41:12
%S A103771 1,4,20,100,496,2464,12240,60800,302016,1500224,7452160,37017600,
%T A103771 183879936,913398784,4537185280,22537856000,111953760256,556115206144,
%U A103771 2762427289600,13721985024000,68162110078976,338586089570304
%N A103771 Expansion of 1/(1-4x-4x^2-4x^3).
%C A103771 The sequence with g.f. 1/(1-r*x-r*x^2-r*x^3) has general term Sum_{k=0..n} T(n-k,k)r^(n-k).
%H A103771 Michael De Vlieger, <a href="/A103771/b103771.txt">Table of n, a(n) for n = 0..1436</a>
%H A103771 Yassine Otmani, <a href="https://cs.uwaterloo.ca/journals/JIS/VOL28/Otmani/otmani10.html">The 2-Pascal Triangle and a Related Riordan Array</a>, J. Int. Seq. (2025) Vol. 28, Issue 3, Art. No. 25.3.5. See p. 19.
%H A103771 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (4,4,4).
%F A103771 a(n) = Sum_{k=0..n} T(n-k, k)4^(n-k), where T(n, k) = trinomial coefficients (A027907).
%t A103771 CoefficientList[Series[1/(1 - 4 x - 4 x^2 - 4 x^3), {x, 0, 21}], x] (* _Michael De Vlieger_, May 07 2025 *)
%Y A103771 Cf. A077828, A077835, A000073.
%K A103771 easy,nonn
%O A103771 0,2
%A A103771 _Paul Barry_, Feb 15 2005