Numbers of the form p^2 - 1 where p is a prime of the form 3*k-1 (A003627).

Terms

a(0) =3a(1) =24a(2) =120a(3) =288a(4) =528a(5) =840a(6) =1680a(7) =2208a(8) =2808a(9) =3480a(10) =5040a(11) =6888a(12) =7920a(13) =10200a(14) =11448a(15) =12768a(16) =17160a(17) =18768a(18) =22200a(19) =27888a(20) =29928a(21) =32040a(22) =36480a(23) =38808a(24) =51528a(25) =54288a(26) =57120a(27) =63000a(28) =66048a(29) =69168