Partial sums of A002620.

Terms

a(0) =0a(1) =0a(2) =1a(3) =3a(4) =7a(5) =13a(6) =22a(7) =34a(8) =50a(9) =70a(10) =95a(11) =125a(12) =161a(13) =203a(14) =252a(15) =308a(16) =372a(17) =444a(18) =525a(19) =615a(20) =715a(21) =825a(22) =946a(23) =1078a(24) =1222a(25) =1378a(26) =1547a(27) =1729a(28) =1925a(29) =2135