⎣ ⎢ ⎢ ⎢ ⎢ ⎢ ⌊ k 2 0 1 6 ⌋ 2 0 1 6 ⎦ ⎥ ⎥ ⎥ ⎥ ⎥ = k ; ⎢ ⎢ ⎢ ⎢ ⎢ ⎡ ⌈ k 2 0 1 6 ⌉ 2 0 1 6 ⎥ ⎥ ⎥ ⎥ ⎥ ⎤ = k
An integer 1 ≤ k ≤ 2 0 1 6 is called 2016-awesome if it satisfies the equations above.
Find the number of 2016-awesome numbers.
This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try
refreshing the page, (b) enabling javascript if it is disabled on your browser and,
finally, (c)
loading the
non-javascript version of this page
. We're sorry about the hassle.
Problem Loading...
Note Loading...
Set Loading...
For the following derivations, we assume that k doesn't divide 2016.
Let j = ⌊ k 2 0 1 6 ⌋ . From the first equation we have that: k + 1 2 0 1 6 < j ≤ k 2 0 1 6 Provided that there is an integer value that j can take in ( k + 1 2 0 1 6 , k 2 0 1 6 ] then eq. 1 will be met. This imples that the first equation must be met if the length of the interval is greater or equal to 1. From this we get:
k 2 0 1 6 − k + 1 2 0 1 6 = k ( k + 1 ) 2 0 1 6 ≥ 1 0 ≥ k 2 + k − 2 0 1 6 2 − 1 − 8 0 6 5 ≤ k ≤ 2 − 1 + 8 0 6 5 k ≤ 4 4
Similarly, letting i = ⌈ k 2 0 1 6 ⌉ . From the second equation we have that: k 2 0 1 6 ≤ i < k − 1 2 0 1 6
By similar reasoning to the previous derivation, we get that:
k − 1 2 0 1 6 − k 2 0 1 6 = k ( k − 1 ) 2 0 1 6 ≥ 1 0 ≥ k 2 − k − 2 0 1 6 2 1 − 8 0 6 5 ≤ k ≤ 2 1 + 8 0 6 5 k ≤ 4 5
We no know that all k ≤ 4 4 satisfy both equations.
Since k doesn't divide 2016, j + 1 = i .
If both equations are met, then necessarily:
⌊ j 2 0 1 6 ⌋ = ⌈ j + 1 2 0 1 6 ⌉ j 2 0 1 6 = j + 1 2 0 1 6 + α
Where 0 < α < 2 . This in turn implies:
α = j ( j + 1 ) 2 0 1 6 j = 2 − 1 + 1 + 8 0 6 4 / α j > 2 − 1 + 1 + 8 0 6 4 / 2 j ≥ 3 2 k ≤ 6 1
Therefore, if k doesn't divide 2016, it can only satisfy both equations if it is less than or equal to 61. We now check the interval 4 4 < k ≤ 6 1 . In it 45, 46, 48, 50, 51, 54 and 56 satisfy both equations. So far, we found 4 4 + 7 = 5 1 cases where both equations are met. The remaining numbers that satisfy the equations are the factors of 2016 that we haven't already counted. These are: 63, 72, 84, 96, 112, 126, 144, 168, 224, 252, 288, 336, 504, 672, 1008 and 2016.
For numbers greater that 2016, eq. one gives ⌊ 0 2 0 1 6 ⌋ = k , so there are no other solutions.
So, in total there are 67 2016-awesome integers.