a(n) = n + (n-1)*(n-2) + (n-3)*(n-4)*(n-5) + (n-6)*(n-7)*(n-8)*(n-9) + ... + ...*(n-n).

Terms

a(0) =0a(1) =1a(2) =2a(3) =5a(4) =10a(5) =17a(6) =32a(7) =61a(8) =110a(9) =185a(10) =316a(11) =557a(12) =986a(13) =1705a(14) =2840a(15) =4661a(16) =7702a(17) =12881a(18) =21620a(19) =35965a(20) =58706a(21) =94217a(22) =150016a(23) =239045a(24) =382670a(25) =614401a(26) =984332a(27) =1564301a(28) =2458810a(29) =3826745