a(n) = Sum_{k=0..floor(n/3)} (-1)^k * binomial(n-1-2*k,k) * binomial(2*n-6*k,n-3*k).

A360294

a(n) = Sum_{k=0..floor(n/3)} (-1)^k * binomial(n-1-2*k,k) * binomial(2*n-6*k,n-3*k).

Terms

    a(0) =1a(1) =2a(2) =6a(3) =20a(4) =68a(5) =240a(6) =864a(7) =3154a(8) =11628a(9) =43196a(10) =161430a(11) =606228a(12) =2285780a(13) =8647738a(14) =32811378a(15) =124804104a(16) =475748330a(17) =1817005536a(18) =6951390372a(19) =26634502642a(20) =102189927918a(21) =392559063268

External references