तस्यापि द्विरथोत्तरा वृद्धिरैकविंशतिरथादिति ॥ कZ_१०.५.१८ ॥
tasyāpi dvirathottarā vṛddhiraikaviṃśatirathāditi
For that (irregular array) too, the increase is by two chariots each step, beginning from twenty-one chariots.
To standardize expansion of formations in predictable steps, aiding planning, command control, and proportional allocation.