a(n) = (prime(n) - 1)*(prime(n+1) - 1)/2 + 3.

Terms

a(0) =4a(1) =7a(2) =15a(3) =33a(4) =63a(5) =99a(6) =147a(7) =201a(8) =311a(9) =423a(10) =543a(11) =723a(12) =843a(13) =969a(14) =1199a(15) =1511a(16) =1743a(17) =1983a(18) =2313a(19) =2523a(20) =2811a(21) =3201a(22) =3611a(23) =4227a(24) =4803a(25) =5103a(26) =5409a(27) =5727a(28) =6051a(29) =7059