a(n) = 1*(n+1-1) + 2*(n+1-2) + ... + k*(n+1-k), where k = floor((n+1)/2).

Terms

a(0) =2a(1) =3a(2) =10a(3) =13a(4) =28a(5) =34a(6) =60a(7) =70a(8) =110a(9) =125a(10) =182a(11) =203a(12) =280a(13) =308a(14) =408a(15) =444a(16) =570a(17) =615a(18) =770a(19) =825a(20) =1012a(21) =1078a(22) =1300a(23) =1378a(24) =1638a(25) =1729a(26) =2030a(27) =2135a(28) =2480a(29) =2600