a(n) = floor((n^2 + n + 8) / 4).

Terms

a(0) =2a(1) =3a(2) =5a(3) =7a(4) =9a(5) =12a(6) =16a(7) =20a(8) =24a(9) =29a(10) =35a(11) =41a(12) =47a(13) =54a(14) =62a(15) =70a(16) =78a(17) =87a(18) =97a(19) =107a(20) =117a(21) =128a(22) =140a(23) =152a(24) =164a(25) =177a(26) =191a(27) =205a(28) =219a(29) =234