collatz_histo.py

mem = {}

def collatz_len(n):
    if n < 2:
        return 1
    if n not in mem:
        chain = 1 + collatz_len(n/2 if n%2 == 0 else 3*n + 1)
        mem[n] = chain
    return mem[n]

def histo_bar(n):
    return '=' * n

X = 13
histo = {n: 0 for n in range(X)}

Y = 1000000
for i in range(Y):
    n = collatz_len(i)
    histo[n % X] += 1

for i in range(X):
    n = int(histo[i] / 1000)
    print(histo_bar(n))