Why does my code to find primes stop working after prime 300?

[joseph terzi]

I am trying to use recursion to calculate the nth prime. It works up until i believe around 300 when the interpreter says "maximum recusrion depth exceeded." Here is the code i wrote.

def program(n): ## initializes
    if n == 1: ## checks for special case of even prime 
        print 2
        return None 
    counter = 1
    index = 3
    nthprime(n, counter, index) ## calls nthprime which takes n, counter index, as arguments 

def nthprime(n, counter, index):
    if counter == n-1 and isprime(index) != None: ## test case
        print index
        return None
    if isprime(index) != None: ## increments counter and sets index to next odd number if index is prime
        counter = counter + 1   
        index = index + 2
    
    else: index = index + 2  ## keeps counter the same and sets index to next odd number if index is not prime
    
    nthprime(n, counter, index)  ## calls nthprime with either the new counter and index or just the new index 
    
def isprime(x):
    
    index = 2 ## variable to check divisors
    while index <= x**.5: ## loop condition of how many divisors to check 
        if x%index == 0: ## if a remainder is found on first index return nothing 
            return None
        
        else: index = index + 1  ## increment index and check again
    return x ## no divisors found less than sqrt x, therefore number is prime

[dwblas]

There is no reason to use recursion for prime numbers. Generally a for() or while() loop is used.
1. Number is 3 or greater and not an even number
2. For loop from 3 to square root + 1 of the number, step=2 to eliminate division by even numbers
3. If division results in no remainder, exit or return from the function