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

Terms

a(0) =1a(1) =1a(2) =1a(3) =-1a(4) =-4a(5) =-10a(6) =-8a(7) =-11a(8) =13a(9) =38a(10) =151a(11) =299a(12) =546a(13) =949a(14) =1649a(15) =2763a(16) =4204a(17) =6746a(18) =10266a(19) =16290a(20) =23536a(21) =36655a(22) =53613a(23) =83391a(24) =123900a(25) =193641a(26) =292867a(27) =460885a(28) =707580a(29) =1120644