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

Terms

a(0) =1a(1) =1a(2) =4a(3) =27a(4) =80a(5) =400a(6) =1908a(7) =6223a(8) =31296a(9) =116478a(10) =450100a(11) =1828915a(12) =7360848a(13) =26906828a(14) =95776772a(15) =403908975a(16) =1421758720a(17) =5072014447a(18) =18481180644a(19) =68350964211a(20) =246180936400a(21) =827642046294