a(n) = 2*A002532(n).

Terms

a(0) =0a(1) =2a(2) =4a(3) =18a(4) =56a(5) =202a(6) =684a(7) =2378a(8) =8176a(9) =28242a(10) =97364a(11) =335938a(12) =1158696a(13) =3997082a(14) =13787644a(15) =47560698a(16) =164059616a(17) =565922722a(18) =1952143524a(19) =6733900658a(20) =23228518936a(21) =80126541162a(22) =276395677004a(23) =953424059818