a(n) = Sum_{k=0..floor(n/4)} binomial(n-1-3*k,k) * binomial(2*n-8*k,n-4*k).

A360292

a(n) = Sum_{k=0..floor(n/4)} binomial(n-1-3*k,k) * binomial(2*n-8*k,n-4*k).

Terms

    a(0) =1a(1) =2a(2) =6a(3) =20a(4) =70a(5) =254a(6) =936a(7) =3492a(8) =13150a(9) =49882a(10) =190318a(11) =729576a(12) =2807816a(13) =10841962a(14) =41983588a(15) =162973568a(16) =633994982a(17) =2471010742a(18) =9646981054a(19) =37718873700a(20) =147676286078a(21) =578883674722

External references