a(n) = Sum_{k=0..floor(n/4)} (-1)^k * binomial(n-3*k,k) * binomial(2*(n-3*k),n-3*k).

A360219

a(n) = Sum_{k=0..floor(n/4)} (-1)^k * binomial(n-3*k,k) * binomial(2*(n-3*k),n-3*k).

Terms

    a(0) =1a(1) =2a(2) =6a(3) =20a(4) =68a(5) =240a(6) =864a(7) =3152a(8) =11616a(9) =43136a(10) =161152a(11) =604992a(12) =2280416a(13) =8624832a(14) =32714688a(15) =124399488a(16) =474066560a(17) =1810053120a(18) =6922776576a(19) =26517173760a(20) =101710338048a(21) =390603984896

External references