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

A360291

a(n) = Sum_{k=0..floor(n/3)} 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) =72a(5) =264a(6) =984a(7) =3714a(8) =14148a(9) =54284a(10) =209482a(11) =812196a(12) =3161340a(13) =12345658a(14) =48348522a(15) =189807336a(16) =746740510a(17) =2943359208a(18) =11620961412a(19) =45950375602a(20) =181936110006a(21) =721233025332

External references