a(n) = floor((10*n^3 + 57*n^2 + 102*n + 72) / 72).

Terms

a(0) =1a(1) =3a(2) =8a(3) =16a(4) =28a(5) =45a(6) =68a(7) =97a(8) =134a(9) =179a(10) =233a(11) =297a(12) =372a(13) =458a(14) =557a(15) =669a(16) =795a(17) =936a(18) =1093a(19) =1266a(20) =1457a(21) =1666a(22) =1894a(23) =2142a(24) =2411a(25) =2701a(26) =3014a(27) =3350a(28) =3710a(29) =4095