SOLUTION: Recall the one-to-one and onto mapping of the set of natural numbers to the set of integers. We used this mapping to show that the integers were countably infinite. Find a function

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Question 1176880: Recall the one-to-one and onto mapping of the set of natural numbers to the set of integers. We used this mapping to show that the integers were countably infinite. Find a function, f(n) that gives the nth integer of the given mapping below. You may find it useful to know that the floor(x) of a number is the largest integer that is less than or equal to x. You may use the floor in your final answer.
Examples: floor(4.3) = 4
floor(10.789) = 10
floor(8) = 8
floor(-2.6) = -3
Mapping:
N Z
1 0
2 1
3 -1
4 2
5 -2
6 3
7 -3
... ...

Answer by ikleyn(52786) About Me  (Show Source):
You can put this solution on YOUR website!
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Recall the one-to-one and onto mapping of the set of natural numbers to the set of integers. We used this mapping to show that the integers were countably infinite. Find a function, f(n) that gives the nth integer of the given mapping below. You may find it useful to know that the floor(x) of a number is the largest integer that is less than or equal to x. You may use the floor in your final answer.
Examples: floor(4.3) = 4
floor(10.789) = 10
floor(8) = 8
floor(-2.6) = -3
Mapping:
N Z
1 0
2 1
3 -1
4 2
5 -2
6 3
7 -3
~~~~~~~~~~~~~~~~~~~~~~~~~~


Use this function

    f: N  --->  Z   from natural numbers (= positive integers) to all integers
  
    f(1) = 0,

    f(n) = %28-1%29%5En * floor%28n%2F2%29%29,  n > = 2.


It maps


      n      1    2    3    4    5    6    7    8    9. . . . 

    f(n)     0    1   -1    2   -2    3   -3    4   -4 . . . 


and so on.

Solved.