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, ...

If you are given any 10 to the power of x and replace the last 0 with a 1 (or add 1), it will be prime. All other numbers like 1101 and 1011 where there is 1 or more 1's between the beginning and the end are NOT prime numbers. They are all divisible by 3.

Posted by Mitch Mullings on 2004-02-22 20:54:46