A superprime is an integer such that all its lefttoright 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 lefttruncatable 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 20101021 12:14:59 