Odious Mersenne exponents.

Terms

a(0) =2a(1) =7a(2) =13a(3) =19a(4) =31a(5) =61a(6) =107a(7) =127a(8) =521a(9) =607a(10) =1279a(11) =3217a(12) =11213a(13) =21701a(14) =44497a(15) =132049a(16) =216091a(17) =756839a(18) =1257787a(19) =3021377a(20) =6972593a(21) =20996011a(22) =24036583a(23) =30402457a(24) =37156667a(25) =43112609a(26) =82589933