a(n) = Sum_{k=0..floor(n/3)} binomial(2*(n-3*k),k) * binomial(2*(n-3*k),n-3*k).

A361753

a(n) = Sum_{k=0..floor(n/3)} binomial(2*(n-3*k),k) * binomial(2*(n-3*k),n-3*k).

Terms

    a(0) =1a(1) =2a(2) =6a(3) =20a(4) =74a(5) =276a(6) =1044a(7) =3994a(8) =15426a(9) =60008a(10) =234764a(11) =922716a(12) =3640700a(13) =14411952a(14) =57210750a(15) =227659704a(16) =907853778a(17) =3627085932a(18) =14515139376a(19) =58174092472a(20) =233463067284a(21) =938061587212

External references