https://oeis.org/A181391

van_eck.py

def van_eck():
    """https://oeis.org/A181391
    """
    seen = {}
    yield 0
    previous, current = 0, None
    i = 1
    while True:
        if previous in seen:
            current = i - seen[previous] - 1
        else:
            current = 0
        yield current
        seen[previous] = i - 1
        previous = current
        i += 1


def test_van_eck():
    from_oeis = (
        "0 0 1 0 2 0 2 2 1 6 0 5 0 2 6 5 4 0 5 3 0 3 2 9 0 4 9 3 6 14 0 6 3 5 "
        "15 0 5 3 5 2 17 0 6 11 0 3 8 0 3 3 1 42 0 5 15 20 0 4 32 0 3 11 18 0 "
        "4 7 0 3 7 3 2 31 0 6 31 3 6 3 2 8 33 0 9 56 0 3 8 7 19 0 5 37 0 3 8 8"
    )
    from_oeis = [int(i) for i in from_oeis.split()]
    for oeis, mine in zip(from_oeis, van_eck()):
        assert oeis == mine


if __name__ == "__main__":
    for i in van_eck():
        print(i)