If is the th prime such that is a Mersenne Prime, then

It was modified by Wagstaff (1983) to yield

where is the Euler-Mascheroni Constant.

**References**

Ribenboim, P. *The Book of Prime Number Records, 2nd ed.* New York: Springer-Verlag, pp. 332-333, 1989.

Wagstaff, S. S. ``Divisors of Mersenne Numbers.'' *Math. Comput.* **40**, 385-397, 1983.

© 1996-9

1999-05-25