Smallest prime factor of A135972(n), the n-th composite Mersenne number.

Terms

a(0) =3a(1) =3a(2) =3a(3) =7a(4) =3a(5) =23a(6) =3a(7) =3a(8) =7a(9) =3a(10) =3a(11) =3a(12) =7a(13) =3a(14) =47a(15) =3a(16) =31a(17) =3a(18) =7a(19) =3a(20) =233a(21) =3a(22) =3a(23) =7a(24) =3a(25) =31a(26) =3a(27) =223a(28) =3a(29) =7