# sum of two equal digit numbers vs. sum of those digits

if I take 5688+6984=12672 then sum the result 1+2+6+7+2=18 then sum that result 1+8=9. vs. this. same digits from above. 5+6+8+8+6+9+8+4=54 then sum that result 5+4=9. using this method where the original two are always the same length, four digits in this example, and always re-summing down to one digit, the result is always the same. Is this significant at all??? than you.

• This is wellknown, as the repeated digit-sum is $9$ if the given positive integer is a multiple of $9$ (and it is the remainder from dividing by $9$ otherwise). – Hagen von Eitzen Oct 30 '14 at 15:58
• Thank you for the feedback, I looked that up just now. Very helpful. – shawn Oct 30 '14 at 16:10

Hint : A number is divisible by $9$ if and only if the sum of its digits is divisible by $9$.