def _numbers_decades(N):
    """
    >>> _numbers_decades(45)
    '         1         2         3         4'
    """
    N = N // 10
    lst = range(1, N + 1)
    return "".join(map(lambda i: "%10s" % i, lst))
>>> _numbers_decades(45)
    '         1         2         3         4'