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Big, super and prime (Posted on 2010-10-20) Difficulty: 4 of 5
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.

No Solution Yet Submitted by Ady TZIDON    
Rating: 3.0000 (2 votes)

Comments: ( Back to comment list | You must be logged in to post comments.)
Solved by hand Comment 8 of 8 |
I built my list by hand with help from to help me add a digit to each of my longest primes.

It makes a nice tree diagram.
The number of superprimes of 1,2,... digits is 4,10,15,18,16,12,8,5,0,0,0,0,0...

I was surprised that not one of the 5 primes of length 8 could be extended.  The largest of them is 73939133.

  Posted by Jer on 2010-10-21 15:39:50
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