1,1

Only four terms are known.

R. K. Guy, Unsolved Problems in Number Theory, 3rd ed., Springer-Verlag, NY, 2004, Sec. A3.

G. H. Hardy and E. M. Wright, An Introduction to the Theory of Numbers, 3rd ed., Oxford Univ. Press, 1954, p. 16.

P. Ribenboim, The New Book of Prime Number Records, Springer-Verlag, NY, 1996, Chap. 2, Sec. VII.

C. K. Caldwell, Mersenne Primes: Conjectures and Unsolved Problems

Eric Weisstein's World of Mathematics, Double Mersenne Number

Wikipedia, Mersenne prime

M(13) = 8191 is a Mersenne prime and M(1891) is composite, so 1891 is a member.

Cf. A000043, A000668, A001348, A077585, A077586, A103901.

Sequence in context: A108093 A051334 A145592 this_sequence A075960 A011563 A075955

Adjacent sequences: A103899 A103900 A103901 this_sequence A103903 A103904 A103905

hard,nonn

Jonathan Sondow (jsondow(AT)alumni.princeton.edu), Feb 20 2005