a(n) = T(2n,n), array T as in A054144.

Terms

a(0) =0a(1) =3a(2) =21a(3) =108a(4) =492a(5) =2100a(6) =8604a(7) =34272a(8) =133728a(9) =513648a(10) =1948560a(11) =7318080a(12) =27256896a(13) =100815936a(14) =370684608a(15) =1355996160a(16) =4938304512a(17) =17914202880a(18) =64760732928a(19) =233390693376a(20) =838784916480