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 A103780 #15 Jun 14 2020 12:23:37
%S A103780 1,1,3,9,25,69,189,519,1428,3930,10812,29742,81816,225070,619156,
%T A103780 1703262,4685565,12889687,35458707,97544655,268339161,738183999,
%U A103780 2030697309,5586319365,15367609920,42275319276,116296719448
%N A103780 Row sums of square of trinomial triangle A071675.
%H A103780 G. C. Greubel, <a href="/A103780/b103780.txt">Table of n, a(n) for n = 0..1000</a>
%H A103780 <a href="/index/Rec#order_09">Index entries for linear recurrences with constant coefficients</a>, signature (1,2,4,6,8,8,6,3,1).
%F A103780 G.f.: 1/(1-x-2*x^2-4*x^3-6*x^4-8*x^5-8*x^6-6*x^7-3*x^8-x^9).
%F A103780 a(n) = a(n-1) +2a(n-2) +4a(n-3) +6a(n-4) +8a(n-5) +8a(n-6) +6a(n-7) +3a(n-8) +a(n-9).
%t A103780 CoefficientList[Series[1/(1 - x - 2*x^2 - 4*x^3 - 6*x^4 - 8*x^5 - 8*x^6 - 6*x^7 - 3*x^8 - x^9), {x,0,50}], x] (* _G. C. Greubel_, Mar 03 2017 *)
%t A103780 LinearRecurrence[{1,2,4,6,8,8,6,3,1},{1,1,3,9,25,69,189,519,1428},40] (* _Harvey P. Dale_, Jun 14 2020 *)
%o A103780 (Maxima)
%o A103780 a(n):=sum(sum((sum(binomial(j,n-3*k+2*j)*(-1)^(j-k)*binomial(k,j),j,0,k)) *sum(binomial(j,-3*m+k+2*j)*binomial(m,j),j,0,m),k,m,n),m,0,n); /* Vladimir Kruchinin, Dec 01 2011 */
%o A103780 (PARI) x='x+O('x^50); Vec(1/(1 -x -2*x^2 -4*x^3 -6*x^4 -8*x^5 -8*x^6 -6*x^7 -3*x^8 -x^9)) \\ _G. C. Greubel_, Mar 03 2017
%K A103780 easy,nonn
%O A103780 0,3
%A A103780 _Paul Barry_, Feb 15 2005