xlabel('n')
ylabel('$\phi(n)$')
plot([None]+[fi(i) for i in range(1,1000)], 'b.')

def fattorizza(n):
    c = 0
    f = {}
    for i in xrange( 2, int(sqrt(n))+1 ):
        if not n%i:
            f[i] = 1
            n /= i
        while not n%i:
            f[i] += 1
            vn = n
            n /= i
        if n == 1:
            return f
    f[n] = 1
    return f

def fi(n):
    if n == 1:
        return 1
    fi = 1
    f = fattorizza(n)
    for p in f:
        k = f[p]
        fi *= (p-1)*p**(k-1)
    return fi