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def is_pow_2(n):
bin_count = 0
while n > 0:
if n % 2 == 1:
bin_count += 1
if bin_count > 1:
return False
n /= 2
return bin_count == 1
def collatz_pow_2(n):
if n == 1: return 4
if n == 2: return 4
collatz_pow_2 = []
while n > 2:
print n,
if is_pow_2(n):
collatz_pow_2.append(n)
if n % 2:
n = n * 3 - 1
else:
n /= 2
return max(collatz_pow_2)
import sys
collatz_pow_2(int(sys.argv[1]))
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