from __future__ import division, print_function   # Python 3

def syracuse(n):
    while n != 1:
        print(n, end=' ')
        if n % 2 == 0:
            n = n//2
        else:
            n = 3*n+1

syracuse(23)

syracuse(245)

syracuse(245154)

def diviseurs(n):
    L = []
    for i in range(1, n+1):
        if n % i == 0:
            L.append(i)
    return L

diviseurs(12)

diviseurs(13)

diviseurs(15)

diviseurs(24)

def est_premier_1(n):
    L = diviseurs(n)
    return len(L) == 2

est_premier_1(12)

est_premier_1(13)

[n for n in range(20) if est_premier_1(n)]

from math import sqrt
def est_premier(n):
    sq = int(sqrt(n))
    for i in range(2, sq):
        if n % i == 0:
            return False
    return True

[n for n in range(20) if est_premier(n)]

from math import sqrt
def est_premier(n):
    sq = int(sqrt(n))
    for i in range(2, sq+1):
        if n % i == 0:
            return False
    return True

[n for n in range(20) if est_premier(n)]

from math import sqrt
def est_premier(n):
    if n == 0 or n == 1:
        return False
    sq = int(sqrt(n))
    for i in range(2, sq+1):
        if n % i == 0:
            return False
    return True

[n for n in range(50) if est_premier(n)]