def week_day_on_first_auroran(dek_year: int) -> int:
    """Returns the Gregorian week day for the first Auroran of a given year

    Args:
        dek_year (int): Year.

    Return:
        int: The week day.
        Example: 1 = Sunday; 2 = Monday; 3 = Tuesday ... 7 = Saturday.
    """
    week_day = (
        (1 + 5 * ((dek_year) % 4) + 4 * ((dek_year) % 100) + 6 * ((dek_year) % 400)) % 7
    ) + 1
    return week_day