a(n) = floor(n^2/2).

Terms

a(0) =0a(1) =0a(2) =2a(3) =4a(4) =8a(5) =12a(6) =18a(7) =24a(8) =32a(9) =40a(10) =50a(11) =60a(12) =72a(13) =84a(14) =98a(15) =112a(16) =128a(17) =144a(18) =162a(19) =180a(20) =200a(21) =220a(22) =242a(23) =264a(24) =288a(25) =312a(26) =338a(27) =364a(28) =392a(29) =420