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

Terms

a(0) =1a(1) =2a(2) =5a(3) =19a(4) =49a(5) =126a(6) =469a(7) =1177a(8) =2881a(9) =6481a(10) =23101a(11) =53725a(12) =127153a(13) =274288a(14) =581925a(15) =1860751a(16) =4155649a(17) =9279791a(18) =19409221a(19) =39839239a(20) =77052401a(21) =229393207a(22) =481747949a(23) =1035561408a(24) =2082441025a(25) =4153434376a(26) =7822058869a(27) =14686515649a(28) =39394280689a(29) =79657493191