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Long chain (Posted on 2015-04-10) Difficulty: 3 of 5
Create a chain of consecutive digits starting with 1 and following 9 by 0: 123456789012345...

How many digits are needed to obtain the 1st prime number?

See The Solution Submitted by Ady TZIDON    
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Hints/Tips re: computer exploration | Comment 2 of 7 |
(In reply to computer exploration by Charlie)

Clearly 2 is not the correct answer, as it does not comply with the definition of the string (in which 9 is followed by 0).

Re your program - only the strings terminating by 1 and 7 are candidates to be tested, since 2,4,6,8 or 0  create  an even number, 5 causes the chain to be divisible by 5, and 3 or 9 at the end result in s.o.d. that is a multiple of 3.

The answer (to the best of my knowledge) over 150 and below 200 digits, and I can provide it to you by Email if your revised rogram fails to discover it. 

Feel free to reach me by Email for clarifications, if needed.


  Posted by Ady TZIDON on 2015-04-10 23:50:31
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