T(2n+4,n), where T is the array in A055830.

Terms

a(0) =5a(1) =30a(2) =162a(3) =850a(4) =4425a(5) =22995a(6) =119560a(7) =622512a(8) =3246750a(9) =16963375a(10) =88779900a(11) =465386220a(12) =2443204946a(13) =12844119225a(14) =67608235800a(15) =356288599640