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8675309 (Posted on 2014-02-26) Difficulty: 3 of 5
Jenny's phone number is 867-5309, according to the song. Here are some problems about the number 8675309.

1. 8675309 is prime. How many prime phone numbers are there if phone numbers are 7 digits and cannot start with 0?

2. How many prime phone numbers are there if phone numbers are 7 digits and can start with 0?

3. 8675309 is the 582161st prime, and 582161 is prime, too. Therefore, 8675309 is a superprime. How many superprimes are ≤8675309?

4. 8675311 is prime. Therefore, 8675309 and 8675311 are twin primes. How many twin prime pairs (n, n+2) are there such that n≤8675309?

See The Solution Submitted by Math Man    
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  Subject Author Date
Solutioncomputer solutionCharlie2014-02-26 17:07:50
SolutionSolutiontomarken2014-02-26 14:41:24
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