History of Hindu Mathematics: A Source Book v1.c8.s10.5

v1.c8.s10.5

The *rationale* of the above rules will be clear from the following: Let $n = d_m d_m-1 d₂ d₁$ be a number of *m* digits written in the decimal place-value notation. Let S₁ denote the sum of its digits, S₂ the sum of the digits of S₁, and so on.