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Binary Primes (Posted on 2004-02-18)

How many primes, written in usual base 10, have digits that are alternating 1s and 0s, beginning and ending with one?

For example (not necessarily prime):
1, 101, 10101, ...

See The Solution Submitted by Aaron

Rating: 3.5000 (2 votes)

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Second thought

| Comment 3 of 13 |

10101 or any number with 3n 1's is divisible by 3

so the # of 1's can't be even (except for 101) or a multiple of 3

Posted by Larry on 2004-02-18 14:25:58

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