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 A327002 #3 Aug 13 2019 09:03:48 %S A327002 0,0,0,10,2574,748616,282846568,141482705378,93129791442534, %T A327002 79703248816409088,87547852413089111888,121899005847224540133690, %U A327002 212656111085108159911203710,459737640779469178164281972792,1218867518038879445116138285206008,3923403293626677106527196012373423122 %N A327002 a(n) = A018893(n) - A291973(n). %p A327002 CL := (f, x) -> PolynomialTools:-CoefficientList(f, x): %p A327002 A327002 := proc(n) local P, Q; %p A327002 P := proc(n) option remember; if n = 0 then return 1 fi; %p A327002 add(binomial(3*n, 3*k+3)*P(n-k-1)*x, k=0..n-1) end: %p A327002 Q := proc(n) option remember; if n = 0 then return 1 fi; %p A327002 add(binomial(3*n-1, 3*k)*Q(k)*Q(n-1-k), k=0..n-1) end: %p A327002 Q(n) - add(CL(P(n),x)[k+1]/k!, k=0..n) end: %p A327002 seq(A327002(n), n=0..15); %Y A327002 Cf. A018893, A291973, row 3 of A327000. %K A327002 nonn %O A327002 0,4 %A A327002 _Peter Luschny_, Aug 13 2019