Eighteen

[rbandrews]

The number 1818 is a number, 18, repeated twice.

If you add together the digits, 1+8+1+8, you also get 18.

There is no other number with this property.

Comments

[desfido.livejournal.com]

What exactly are you considering to be "this property"? Since, for example, I'd say that what you showed is a consequence of the following property which I conjecture: if you have 9y, and repeat the digits of 9y y times, the sum of the digits is 9y, for either any natural number y (using the "0 is not a natural number" version). If I get bored enough waiting to see somebody at the health center later, or in one of my classes, I may go ahead and see if I can prove that, in fact, or figure out what is special about the natural numbers for which it is true (since it's clearly true for a bunch of them).

Anyway, point is, what specifically is the property which you are asserting 1818 uniquely holds? The main contender I can think of is equivalent to the less interesting "1000x+100y+10x+y=1818 and 2x+2y=10x+y, if and only if x=1 and y=8".

[gigaclon.livejournal.com]

yes this is true, but only in base-10 in base-16 1818 adds up to 6 and the number 1818 is impossible in base-2 and base-8