Semiprimes that are a product of Mersenne primes.

Terms

a(0) =9a(1) =21a(2) =49a(3) =93a(4) =217a(5) =381a(6) =889a(7) =961a(8) =3937a(9) =16129a(10) =24573a(11) =57337a(12) =253921a(13) =393213a(14) =917497a(15) =1040257a(16) =1572861a(17) =3670009a(18) =4063201a(19) =16252897a(20) =16646017a(21) =66584449a(22) =67092481a(23) =1073602561a(24) =4294434817a(25) =6442450941a(26) =15032385529a(27) =17179607041