a(n) = 2*a(n-1) + (n-2)*a(n-2) with a(0) = 1, a(1) = 2.

Terms

a(0) =1a(1) =2a(2) =4a(3) =10a(4) =28a(5) =86a(6) =284a(7) =998a(8) =3700a(9) =14386a(10) =58372a(11) =246218a(12) =1076156a(13) =4860710a(14) =22635292a(15) =108459814a(16) =533813716a(17) =2694524642a(18) =13930068740a(19) =73667056394a(20) =398075350108