a(n) = [x^n] Product_{k=1..n} (1 + (n - k + 1)*x^k).

Terms

a(0) =1a(1) =1a(2) =1a(3) =7a(4) =9a(5) =23a(6) =148a(7) =221a(8) =526a(9) =1040a(10) =6767a(11) =9664a(12) =23456a(13) =43943a(14) =91363a(15) =499028a(16) =736410a(17) =1650395a(18) =3107540a(19) =6210372a(20) =10819270a(21) =57864166a(22) =80663444a(23) =179915133a(24) =324882691a(25) =640398244a(26) =1087149284a(27) =2039724322a(28) =9121580902a(29) =12913282685