[seqfan] Fwd: Right truncatable primes

Olivier Gerard olivier.gerard at gmail.com
Tue Oct 28 18:31:35 CET 2008

Hello seqfans,

This is a recent post in the Number Theory List
which might be of interest to member.

Please, put Kurt Foster in copies of your answers
to the list.


---------- Forwarded message ----------
From: Kurt Foster <drsardonicus at earthlink.net>
Date: Tue, Oct 28, 2008 at 18:25
Subject: Right truncatable primes
To: NMBRTHRY at listserv.nodak.edu

I recently revived an interest in these things (which I'll call
rtp's), and Phil Carmody has made some heroic computations to find the
number of base-b rtp's for a steadily-increasing list of b's.

A list of the number of base-b rtps up to base fifty-three is listed
in the OEIS at


There is also a paper,

Angell, I. O. and Godwin, H. J. "On Truncatable Primes." Math. Comput.
31, 265-267, 1977.

I don't have access to electronic archives, so I was wondering if
someone could get me at least a summary of what's in that paper.

I concocted a ridiculously simple model to estimate the number of base-
b rtp's with k digits in terms of b and k.  I was very surprised at
how well it estimated the value of k for which the number of k-digit
rtp's is a maximum, and also the largest k for which there are any k-
digit base-b rtp's.  It's not bad but also not terribly good at
estimating the total number of base-b rtp's in terms of b, but I
figured that before trying to refine my model, I should make sure I
wasn't just re-inventing the wheel.

If anyone knows the above-mentioned paper, or of any more recent work
on these beasties, please let me know.

Thanks, KF

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