recaman.py

import sys
from itertools import count, islice


def sequence():
    """Generate Recaman's sequence."""
    seen = set()
    a = 0
    for n in count(1):
        yield a
        seen.add(a)
        c = a - n
        if c < 0 or c in seen:
            c = a + n
        a = c


def write_sequence(filename, num):
    """Write Recaman's sequence to a text file."""
    with open(filename, mode='wt', encoding='utf-8') as f:
        # generator expression converts each number to a string
        # and adds a new line
        f.writelines("{0}\n".format(r) for r in islice(sequence(), num + 1))

if __name__ == '__main__':
    write_sequence(filename=sys.argv[1], num=int(sys.argv[2]))