Adding Numbers

[ImLostAgain]

I didn't know which section to put this into so I put it here.
Is there a name for the branch of maths whereby you keep adding numbers together until you get a single number?
F'rinstance the year 1949 added would be 23 which added would be 5.

[ImLostAgain]

Never mind, I've remembered.

[murraymints]

ocd !!! lol

[hc4361]

Okay, what's the answer?

[jim360]

You could call it the "digital root".

[ImLostAgain]

Ocd indeed :)
Digital root is what was swimming around in my mind but it was 'summing digits' I was looking for.

[hc4361]

Thank you

[Bazile]

//F'rinstance the year 1949 added would be 23 which added would be 5.//

I do not get it

By the way that is curious - 'F'rinstance'
Why ' instead of o ?

[gingejbee]

....hardly a "branch of maths" though, is it?

[Old_Geezer]

1+9+4+9 added would be 23
2+3 added would be 5

[beso]

It isn't a branch of maths because the results are meaningless. Essentially it is numerology which has no relationship to maths.

Real maths operates at levels quite independent of the base system numerals used to express it.

[jim360]

It's not totally useless -- the digital root is a useful test for divisibility by three or nine, and understanding why that is allows you in principle to extend the approach to testing for divisibility by other numbers or in other bases. Indeed, on a personal note, my second interview for entry into the Maths Course at Cambridge was about exactly this, so it wasn't entirely useless then either.

[beso]

jim, isn't it just an artefact of the base ten system?

[jim360]

To test for divisibility by 9, sure, but in a general base b the digital root allows to test if a number is divisible by (b-1). These days you could also just, you know, enter the division into a calculator. But playing around with digital roots can be educational if done in the right way.

Attaching any meaning beyond that is indeed meaningless numerology though.