'Thirty' in the Bible

These constitute the list of the mighty men whom David had: Jashobeam, the son of a Hachmonite, the chief of the thirty; he lifted up his spear against three hundred whom he killed at one time.

Now three of the thirty chief men went down to the rock to David, into the cave of Adullam, while the army of the Philistines was camping in the valley of Rephaim.

As for Abshai the brother of Joab, he was chief of the thirty, and he swung his spear against three hundred and killed them; and he had a name as well as the thirty.

Behold, he was honored among the thirty, but he did not attain to the three; and David appointed him over his guard.

Adina the son of Shiza the Reubenite, a chief of the Reubenites, and thirty with him,

and Ishmaiah the Gibeonite, a mighty man among the thirty, and over the thirty. Then Jeremiah, Jahaziel, Johanan, Jozabad the Gederathite,

Then the Spirit came upon Amasai, who was the chief of the thirty, and he said,“We are yours, O David,And with you, O son of Jesse!Peace, peace to you,And peace to him who helps you;Indeed, your God helps you!”Then David received them and made them captains of the band.

The Levites were numbered from thirty years old and upward, and their number by census of men was 38,000.

This Benaiah was the mighty man of the thirty, and had charge of thirty; and over his division was Ammizabad his son.