[seqfan] Kind of truncatable sequence
Eric Angelini
Eric.Angelini at kntv.be
Wed Jan 21 18:34:53 CET 2009
Hello SeqFans,
In reading A024770 (Right-truncatable primes: every
prefix is prime)...
[http://www.research.att.com/~njas/sequences/A024770]
... I've had the idea of an monotonically increasing
sequence S like this:
S = 2,3,5,7,29,31,59,71,293,313,593,719,2939,3137,5939,
7193,29399,31379,59393,71933,293999,313797,593933,719333,
2939999,3137977,5939333.
... which is finite and stops there.
Definition: "Erase the last digit of every prime of S;
the result reproduces S without it's last terms"
We know that this kind of sequence is finite, as the
biggest right-truncatable prime is 73939133.
Question:
What could be the longest such sequence (in term of
quantity of integers)?
---
P.-S.
One could see the above sequence of primes like this:
S = 2, 3, 5, 7,
29, 31, 59, 71,
293, 313, 593, 719,
2939, 3137, 5939, 7193,
29399, 31379, 59393, 71933,
293999, 313797, 593933, 719333,
2939999,3137977,5939333 STOP
---
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