Prime

Puzzles

• 101How many primes are in the sequence 101, 10101, 1010101, ...?
• all.prefixWhat is the longest prime whose every proper prefix is a prime?
• change.oneWhat is the smallest number that cannot be made prime by changing a single digit?
• prefix.one2 is prime, but 12, 22, ..., 92 are not.
• square.difference266117 is a prime number. New