a(n) = floor(n^2/12 + 5/4).

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =2a(5) =3a(6) =4a(7) =5a(8) =6a(9) =8a(10) =9a(11) =11a(12) =13a(13) =15a(14) =17a(15) =20a(16) =22a(17) =25a(18) =28a(19) =31a(20) =34a(21) =38a(22) =41a(23) =45a(24) =49a(25) =53a(26) =57a(27) =62a(28) =66a(29) =71