'Twenty' in the Bible

Darius was pleased to put over the kingdom a hundred and twenty captains, who were to be all through the kingdom;

And on the twenty-fourth day of the first month I was by the side of the great river;

But the angel of the kingdom of Persia put himself against me for twenty-one days; but Michael, one of the chief angels, came to my help; and when I came he was still there with the angel of the kings of Persia.