द्विगुणो द्वितीयं त्रिगुनस्तृतीयम् ॥ कZ_०७.१८.०९ ॥
dviguṇo dvitīyaṃ triguṇas tṛtīyam
The second (ally) makes it double; the third makes it triple.
It functions as strategic shorthand: additional reliable partners increase capability disproportionately by adding troops, fronts, logistics, and legitimacy.