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

(In reply to Answer by Old Original Oskar!)

8457=6*1409+3 so 2^8457=((2^6)^1409)*2^3. Since 2^6=64 is congruent to 1 mod 9, 2^8457 is congruent to 2^3=8 mod 9, not 4. Daniel's result is correct, but you are off by 1 in the count that you made to get to your incorrect answer of 4.

Posted by Richard on 2006-06-29 15:08:04