Sum(prime(k),k=1..n)^2-1.

Terms

a(0) =3a(1) =24a(2) =99a(3) =288a(4) =783a(5) =1680a(6) =3363a(7) =5928a(8) =9999a(9) =16640a(10) =25599a(11) =38808a(12) =56643a(13) =78960a(14) =107583a(15) =145160a(16) =193599a(17) =251000a(18) =322623a(19) =408320a(20) =506943a(21) =625680a(22) =763875a(23) =927368a(24) =1123599a(25) =1347920a(26) =1597695a(27) =1879640a(28) =2190399a(29) =2537648