Vestanam Sutra

"Vestanam," which means "By Osculation," is a powerful technique for divisibility tests, especially for prime numbers. It allows us to break down a large number into a smaller one that's easier to check.

The "Osculator" Rule 🌊

To test divisibility, we repeatedly multiply the last digit of our number by a special number (the "osculator") and add/subtract it from the rest of the number.

Example: Is 245 Divisible by 7?

1. Find the Osculator for 7: The osculator for 7 is -2 (a negative osculator).
2. First Osculation: Take the last digit of 245 (5). Multiply by -2: 5 × -2 = -10. Subtract from the rest (24): 24 - 10 = 14.
3. Check the Result: Is 14 divisible by 7? Yes!
4. Conclusion: Since the result is divisible by 7, the original number 245 is also divisible by 7.