Euclid-Mullin Sequence

The sequence of numbers obtained by letting , and defining

where  is the least prime factor. The first few terms are 2, 3, 7, 43, 13, 53, 5, 6221671, 38709183810571, 139, ... (OEIS A000945). Only 43 terms of the sequence are known; the 44th requires factoring a composite 180-digit number.

REFERENCES:

Guy, R. K. and Nowakowski, R. "Discovering Primes with Euclid." Delta (Waukesha) 5, 49-63, 1975.

Mullin, A. A. "Recursive Function Theory." Bull. Amer. Math. Soc. 69, 737, 1963.

Naur, T. "Mullin's Sequence of Primes Is Not Monotonic." Proc. Amer. Math. Soc. 90, 43-44, 1984.

Sloane, N. J. A. Sequence A000945/M0863 in "The On-Line Encyclopedia of Integer Sequences."

Wagstaff, S. S. "Computing Euclid's Primes." Bull. Institute Combin. Applications 8, 23-32, 1993.