Yay for... 2015?

Algebra Level 5

Find the number of functions f f that map non-negative integers to non-negative integers such that

f ( f ( x ) ) = x + 2015. f(f(x)) = x + 2015.

Notes:

By map non-negative integers to non-negative integers , we mean that the domain and range of f f are both the set of non-negative integers.


The answer is 0.

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1 solution

Pranjal Jain
Dec 4, 2014

f ( f ( x ) ) = x + 2015 f(f(x))=x+2015

Substitute x = 2015 x=2015 , f ( f ( f ( x ) ) ) = f ( x ) + 2015 f(f(f(x)))=f(x)+2015 f ( x + 2015 ) = f ( x ) + 2015 f(x+2015)=f(x)+2015

Now it is clear that no function is possible such that it satisfies this equation and map non-negative integers to non-negative integers.

What about a linear function, does it satisfy the above condition .

Akshay Sharma - 5 years, 5 months ago

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