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 A182015 #12 Feb 01 2021 10:17:41
%S A182015 1,2,5,11,26,60,145,353,884,2241,5786,15108,39941,106558,286809,
%T A182015 777505,2121668,5822287,16059288,44494738,123782207,345615047,
%U A182015 968211110,2720561790,7665640267,21654105734,61312389677,173978404587,494667697706,1409099662020
%N A182015 Diagonal sums of triangle A182013.
%F A182015 a(n) = sum(sum(M(i),i=k..n-k),k=0..n), where the M(n)'s are the Motzkin numbers.
%F A182015 a(n) = sum((n-i+1)*M(i),i=0..n) - sum((n-2*i)*M(i),i=0..floor(n/2)).
%F A182015 G.f.: (1-x+x*sqrt(1-2*x-3*x^2)-sqrt(1-2*x^2-3*x^4))/(2*x^3*(1-x)^2).
%t A182015 M[n_]:=If[n==0,1,Coefficient[(1+x+x^2)^(n+1),x^n]/(n+1)]; Table[Sum[(n-i+1)M[i],{i,0,n}]-Sum[(n-2i)M[i],{i,0,Floor[n/2]}],{n,0,30}]
%o A182015 (Maxima) M(n):=coeff(expand((1+x+x^2)^(n+1)),x^n)/(n+1);
%o A182015 makelist(sum((n-i+1)*M(i),i,0,n)-sum((n-2*i)*M(i),i,0,floor(n/2)),n,0,30);
%Y A182015 Cf. A182013.
%K A182015 nonn
%O A182015 0,2
%A A182015 _Emanuele Munarini_, Apr 06 2012