Check if the Civic Registration number for Norway is valid

 private static readonly int[] WeightsNoK1 = new[] { 3, 7, 6, 1, 8, 9, 4, 5, 2 };
    private static readonly int[] WeightsNoK2 = new[] { 5, 4, 3, 2, 7, 6, 5, 4, 3, 2 };

    public bool IsCivicRegistrationNumberValid(string civicNumber)
    {
        if (civicNumber == null)
            return false;

        var cleanedCivicNumber = civicNumber.Replace("-", "");

        if (!IsNumeric(cleanedCivicNumber))
            return false;

        if (cleanedCivicNumber.Length != 11)
            return false;

        if (!IsDateValid(cleanedCivicNumber.Substring(0, 6), "ddMMyy", "nb-NO"))
            return false;

        int sum = 0;
        for (int i = 0; i < 9; i++)
        {
            sum += WeightsNoK1[i] * int.Parse(cleanedCivicNumber.Substring(i, 1));
        }
        int k1 = 11 - sum % 11;
        if (k1 == 11)
        {
            k1 = 0;
        }

        if (k1.ToString() != cleanedCivicNumber.Substring(9, 1))
        {
            return false;
        }

        sum = 0;
        for (int i = 0; i < 10; i++)
        {
            sum += WeightsNoK2[i] * int.Parse(cleanedCivicNumber.Substring(i, 1));
        }

        int k2 = 11 - sum % 11;
        if (k2 == 11)
        {
            k2 = 0;
        }

        if (k2.ToString() != cleanedCivicNumber.Substring(10, 1))
        {
            return false;
        }

        return true;
    }
}