Numbers k for which 2*k-1, 4*k-1, 8*k-1 and 16*k-1 are primes.

Terms

a(0) =3a(1) =45a(2) =90a(3) =180a(4) =255a(5) =615a(6) =705a(7) =1350a(8) =1770a(9) =3225a(10) =5295a(11) =5775a(12) =5955a(13) =6060a(14) =8580a(15) =9855a(16) =9945a(17) =11175a(18) =13095a(19) =13740a(20) =15195a(21) =21825a(22) =26820a(23) =26925a(24) =27615a(25) =28920a(26) =30075a(27) =30705a(28) =31710a(29) =33375