'Thirty' in the Bible

This is the number 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 and killed them at one time.

Three of the thirty chief men went down to the rock to David, into the cave of Adullam; and the army of the Philistines were encamped in the valley of Rephaim.

Behold, he was more honorable than the thirty, but he didn't attain to the [first] three: and David set 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, and Jeremiah, and Jahaziel, and Johanan, and Jozabad the Gederathite,

Then the Spirit came on Amasai, who was chief of the thirty, [and he said], "We are yours, David, and on your side, you son of Jesse: peace, peace be to you, and peace be to your helpers; for your God helps you." Then David received them, and made them captains of the band.

of the sons of Gershom, Joel the chief, and his brothers one hundred thirty;

The Levites were numbered from thirty years old and upward: and their number by their polls, man by man, was thirty-eight thousand.

This is that Benaiah, who was the mighty man of the thirty, and over the thirty: and [of] his division was Ammizabad his son.