Floor(7n^2/2) + floor(5n/2) + floor(3n/7).

Terms

a(0) =5a(1) =19a(2) =39a(3) =67a(4) =101a(5) =143a(6) =191a(7) =247a(8) =308a(9) =379a(10) =454a(11) =539a(12) =628a(13) =727a(14) =830a(15) =942a(16) =1060a(17) =1186a(18) =1318a(19) =1458a(20) =1604a(21) =1758a(22) =1917a(23) =2086a(24) =2259a(25) =2442a(26) =2629a(27) =2826a(28) =3027a(29) =3237