a(n) = (-1 + prime(n+1)^2)/4.

Terms

a(0) =2a(1) =6a(2) =12a(3) =30a(4) =42a(5) =72a(6) =90a(7) =132a(8) =210a(9) =240a(10) =342a(11) =420a(12) =462a(13) =552a(14) =702a(15) =870a(16) =930a(17) =1122a(18) =1260a(19) =1332a(20) =1560a(21) =1722a(22) =1980a(23) =2352a(24) =2550a(25) =2652a(26) =2862a(27) =2970a(28) =3192a(29) =4032