Ekanyunena Purvena
By one less than the previous one (e · ka · nyū · ne · na pūr · ve · na)
What it means
Multiply by 9, 99, 999 — any number made entirely of nines — in two steps. The left half of the answer is one less than your number. The right half completes from 9.
Worked example
Compute 234 × 999. Left half: 234 − 1 = 233. Right half: each digit of 233 subtracted from 9 → (9−2)(9−3)(9−3) = 766. Stick them together: 233766.