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From: eklhad@ihnet.UUCP (K. A. Dahlke)
Newsgroups: net.math
Subject: Another Prime Number Question With No Practical Application
Message-ID: <226@ihnet.UUCP>
Date: Tue, 7-May-85 09:33:31 EDT
Article-I.D.: ihnet.226
Posted: Tue May  7 09:33:31 1985
Date-Received: Wed, 8-May-85 04:50:41 EDT
Distribution: net
Organization: AT&T Bell Laboratories
Lines: 14

< and other diversionary tactics >
	How many primes, when written in base 10,
also produce prime sub-numbers (looking at the first n digits)?
For example: 7193 is in the set, since
7, 71, 719, and 7193 are all prime.
The list begins: 3, 5, 7, 31, 37, 53, 59, 71, 73, 79, 
311, 313, 317, 373, 379, 593, 599, ...
Is the list infinite?
If so, can anyone prove it.
If not, and I conjecture not, what is the largest such number?
Anyone with some time (personal and computer) can enjoy this one.
-- 

Karl Dahlke    ihnp4!ihnet!eklhad