a(n) = a(n-1) + a(n-2) - n*a(floor(n/2)), where a(0) = 1, a(1) = 2, a(2) = 3.

Terms

a(0) =1a(1) =2a(2) =3a(3) =-1a(4) =-10a(5) =-26a(6) =-30a(7) =-49a(8) =1a(9) =42a(10) =303a(11) =631a(12) =1294a(13) =2315a(14) =4295a(15) =7345a(16) =11624a(17) =18952a(18) =29820a(19) =47974a(20) =71734a(21) =113345a(22) =171197a(23) =270029a(24) =410170a(25) =647849a(26) =997829a(27) =1583173a(28) =2460742a(29) =3919360