G.f. satisfies A(x) = 1 + 2*x + 2*x^3*A(x)^3.

Terms

a(0) =1a(1) =2a(2) =0a(3) =2a(4) =12a(5) =24a(6) =28a(7) =120a(8) =480a(9) =1056a(10) =2304a(11) =8448a(12) =27760a(13) =69600a(14) =191232a(15) =643104a(16) =1978560a(17) =5470080a(18) =16353792a(19) =52557312a(20) =159694848a(21) =468853760a(22) =1444300800a(23) =4549644288a(24) =13905927936a(25) =42219904512a(26) =131505807360a(27) =411672307200