Triangular numbers of the form 2p-1 where p is prime.

Terms

a(0) =3a(1) =21a(2) =45a(3) =105a(4) =253a(5) =325a(6) =465a(7) =561a(8) =861a(9) =1081a(10) =1225a(11) =1485a(12) =1653a(13) =1953a(14) =3741a(15) =4005a(16) =4753a(17) =6441a(18) =7021a(19) =7381a(20) =8001a(21) =9045a(22) =10153a(23) =13041a(24) =15753a(25) =19701a(26) =20301a(27) =21945a(28) =23005a(29) =23653