The digital root of a number is obtained by summing its digits and then repeating the process (summing the sum's digits) until the answer is a single digit number. For example, the digital root of 7368 is 6.

Determine the digital root of (9⁷²⁴⁰+38)⁸⁴⁵⁷

A digital root is the remainder of a number divided by 9, so we can ignore 9^7240, and just calculate the remainder of 2^8457, since 38=2+a multiple of 9.

The powers of 2, modulus 9, starting from 0, are 1, 2, 4, 8, 7, 5, 1, 2, 4, 8, 7, 5, ..., so for 8457, we'd get 4 as the answer.

Posted by Old Original Oskar! on 2006-06-29 14:33:30