a(n) = (prime(n)-1)*(prime(n)+1)/6.

Terms

a(0) =4a(1) =8a(2) =20a(3) =28a(4) =48a(5) =60a(6) =88a(7) =140a(8) =160a(9) =228a(10) =280a(11) =308a(12) =368a(13) =468a(14) =580a(15) =620a(16) =748a(17) =840a(18) =888a(19) =1040a(20) =1148a(21) =1320a(22) =1568a(23) =1700a(24) =1768a(25) =1908a(26) =1980a(27) =2128a(28) =2688a(29) =2860