No...what I mean is for example, the number 396 is divisible by 9 because the sum of the digits, which is 9 (3+9+6=18; 1+8=9) is divisible by 9. There is a word for that sum...I can't remember it or find it. Need it for a blog post.

(To swalker2001)
its called a "digit sum"... get you're google-fu up.. this service is more for people who are away from their pcs... sure we'll help each other with some tricky stuff now and then... put try searching for it yourself first

(To swalker2001)
plus you said "repeated summation"... that's not the same thing as adding up the digits in a number... "repeated" threw me off

(To bigmike)
I have searched all over. That is not the term. Surely someone will know this. A mathematician, possibly.

(To bigmike)
It is repeated. If you have a very large number, the first sum you come up with might still be several digits long. So you sum them again and again until you get a single digit number. That sum is what I need the term for. There is a word for it.

I apologize if I didn't make it clear enough in the original question.

(To swalker2001)
google "digit sum"... that's the term for adding the digits of a number... not sure of the second part

(To swalker2001)
how would you get to a single digit from adding large numbers? that makes no sense

(To bigmike)
I found it. This was an excedingly difficult task. The word only appears in one citation that I can find anywhere on the 'net, and I had to use the Wayback Machine to find it. The word is "unitate." Here is an old math text with complete discussion:

http://www.archive.org/stream/elementsofbusine00bigerich/elementsofbusine00bigerich_djvu.txt

Here is a short quote from the text:

"To find the unitate of 87,564,892, add the digits and their sum is 49; adding these gives 13, and adding these gives 4, the unitate."

Now that I know the word, and how it has fallen into complete disuse, I may not use it after all. I will probably say "digit sum."

(To swalker2001)
yea thats an old method of verifying the adding of very large numbers... completely obsolete with the advent of computers... not sure what you're going to use this concept for anyway nowadays

(To bigmike)
Just a simple way for kids to check their math when they don't have a calculator/computer handy. check my blog in a day or two and the post will be there.

Hahaa, nice one! Did you know that or look it up?