data/problems/329.yml
---
:id: 329
:name: Prime Frog
:url: https://projecteuler.net/problem=329
:content: "Susan has a prime frog. \nHer frog is jumping around over 500 squares
numbered 1 to 500. He can only jump one square to the left or to the right, with
equal probability, and he cannot jump outside the range [1;500]. \n(if it lands
at either end, it automatically jumps to the only available square on the next move.)\n\nWhen
he is on a square with a prime number on it, he croaks 'P' (PRIME) with probability
2/3 or 'N' (NOT PRIME) with probability 1/3 just before jumping to the next square.
\ \nWhen he is on a square with a number on it that is not a prime he croaks 'P'
with probability 1/3 or 'N' with probability 2/3 just before jumping to the next
square.\n\nGiven that the frog's starting position is random with the same probability
for every square, and given that she listens to his first 15 croaks, what is the
probability that she hears the sequence PPPPNNPPPNPPNPN?\n\nGive your answer as
a fraction p/q in reduced form.\n"