a(n) = floor(5*n^2/2).

Terms

a(0) =0a(1) =2a(2) =10a(3) =22a(4) =40a(5) =62a(6) =90a(7) =122a(8) =160a(9) =202a(10) =250a(11) =302a(12) =360a(13) =422a(14) =490a(15) =562a(16) =640a(17) =722a(18) =810a(19) =902a(20) =1000a(21) =1102a(22) =1210a(23) =1322a(24) =1440a(25) =1562a(26) =1690a(27) =1822a(28) =1960a(29) =2102