n*A000084(n).

Terms

a(0) =1a(1) =4a(2) =12a(3) =40a(4) =120a(5) =396a(6) =1260a(7) =4176a(8) =13788a(9) =46240a(10) =155496a(11) =527160a(12) =1792804a(13) =6125028a(14) =20986020a(15) =72117632a(16) =248396792a(17) =857402748a(18) =2964896876a(19) =10269550040a(20) =35622420288a(21) =123727866768a(22) =430254861944