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

A360295

a(n) = Sum_{k=0..floor(n/4)} (-1)^k * 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) =250a(6) =912a(7) =3372a(8) =12590a(9) =47362a(10) =179230a(11) =681528a(12) =2601896a(13) =9966798a(14) =38288420a(15) =147453664a(16) =569092438a(17) =2200577502a(18) =8523612766a(19) =33064771524a(20) =128438624798a(21) =499525018638

External references