def listPrimes(nmax):
    # return a list of all primes < nmax by a fairly dumb algorithm
    primes = [2]
    for n in range(3, nmax):
        isPrime = True
        for p in primes:
            if n%p == 0:
                isPrime = False
                break
        if isPrime:
            primes.append(n)

    return primes