I thought coming up with primes would be very challenging, but then my first three guesses were all prime (all I did was pick numbers that ended with odd numbers that weren't five). I got it on the fourth after a few attempts at entering the number - the prime constraint here makes it easier.

There are 8,363 five digit primes. If you limit your guesses to numbers ending in 1, 3, 7, and 9, there is a 23% chance of randomly picking a prime.