Akshauhini number

"Sauti said, 'One chariot, one elephant, five foot-soldiers, and three horses form one Patti; three pattis make one Sena-mukha; three sena-mukhas are called a Gulma; three gulmas, a Gana; three ganas, a Vahini; three vahinis together are called a Pritana; three pritanas form a Chamu; three chamus, one Anikini; and an anikini taken ten times forms, as it is styled by those who know, an Akshauhini.

O ye best of Brahmanas, arithmeticians have calculated that the number of chariots in an Akshauhini is twenty-one thousand eight hundred and seventy. The measure of elephants must be fixed at the same number. O ye pure, you must know that the number of foot-soldiers is one hundred and nine thousand, three hundred and fifty, the number of horse is sixty-five thousand, six hundred and ten. These, O Brahmanas, as fully explained by me, are the numbers of an Akshauhini as said by those acquainted with the principles of numbers. O best of Brahmanas, according to this calculation were composed the eighteen Akshauhinis of the Kaurava and the Pandava army.

Adi Parva Section II