A superprime is an integer such that all its left-to-right initial segments are prime (e.g. 7331 whose segments are 7, 73, 733, and 7331, all prime).
There is a largest superprime.

Find it.

Source: USA Computing Olympiad, Feb 1995.

(In reply to re(3): Another method. -- solution for that Euler problem 37 by Charlie)

 Charlie,

It is said that there are 4260 left-truncatable primes, if zeros are excluded: 357686312646216567629137 is the largest -
(sequence A024785 in OEIS). If zeros are allowed then the length is infinite; e.g. 1000000000000000000000007, 1000000000000000000000000000000000000000000000000000000000007
100000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000007

etc.

Edited on October 21, 2010, 12:47 pm

Posted by broll on 2010-10-21 12:14:59