a(n) = 1*(n+3-1) + 2*(n+3-2) + .... + k*(n+3-k), where k=floor((n+1)/2).

Terms

a(0) =3a(1) =4a(2) =13a(3) =16a(4) =34a(5) =40a(6) =70a(7) =80a(8) =125a(9) =140a(10) =203a(11) =224a(12) =308a(13) =336a(14) =444a(15) =480a(16) =615a(17) =660a(18) =825a(19) =880a(20) =1078a(21) =1144a(22) =1378a(23) =1456a(24) =1729a(25) =1820a(26) =2135a(27) =2240a(28) =2600a(29) =2720