I have to solve that equation :

11n-2n=k2

where n,k are from N .

Well by observation n=1, k=3 is one solution. I don't think there are other solutions but I have no way of proving their aren't

Yes , I have also find that . And n can be also =0 and k=0 .
So there are only 2 solutions,I think .. but how should I demonstrate ?

0 is generally not considered a natural number

Originally Posted by Shakarri
0 is generally not considered a natural number
"There is no universal agreement about whether to include zero in the set of natural numbers: some define the natural numbers to be the positive integers {1, 2, 3, ...}, while for others the term designates the non-negative integers {0, 1, 2, 3, ...}. The former definition is the traditional one, with the latter definition having first appeared in the 19th century. Some authors use the term natural number to exclude 0 and whole number to include it; others use whole number in a way that includes both 0 and the negative integers, i.e., as an equivalent of the integer term."

See this web entry.

I have a great many different textbooks on set theory. In the vast majority of them use $0\in\mathbb{N}$.

It's one of the things in mathematics that irks me

I have a great many different textbooks on set theory. In the vast majority of them use $0\in\mathbb{N}$.