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

A360267

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

Terms

    a(0) =1a(1) =2a(2) =6a(3) =20a(4) =72a(5) =264a(6) =984a(7) =3712a(8) =14136a(9) =54224a(10) =209200a(11) =810912a(12) =3155616a(13) =12320512a(14) =48239232a(15) =189336192a(16) =744722400a(17) =2934759360a(18) =11584470336a(19) =45796087680a(20) =181285742592a(21) =718498695424

External references