In calculus, when you take the derivative of a constant you get zero as an answer. In number theory, there is something called the arithmetic derivative which allows you to differentiate a number and get a nonzero answer. The arithmetic derivative works as follows.
Where denotes the arithmetic derivative of :
for all primes
For example,
Let us define the Logarithmic Arithmetic Derivative , denoted by , as . For how many ordered pairs , where and are distinct positive integers less than , does ?
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.
a = b is a trivial solutions. For a = b L ( a ) = L ( b ) a a ′ = b b ′ a ′ b − b ′ a = 0 b 2 a ′ b − b ′ a = 0 ( b a ) ′ = 0 From solution to this problem , if b a = ∏ i = 1 k p i x i then ( b a ) ′ = b a i = 1 ∑ k p i x i Now for this problem ( b a ) ′ = b a i = 1 ∑ k p i x i = 0 i = 1 ∑ k p i x i = 0 x 1 p 2 p 3 . . . p k + x 2 p 1 p 3 . . . p k + . . . + x k p 1 p 2 . . . p k = 0 ⋆ In the same manner of solution to above mentioned problem one can conclude that x i = c i p i and equation ⋆ becomes c 1 + c 2 + . . . + c k = 0 . Therefore the solutions to the equation ( b a ) ′ = 0 † are in the form b a = i = 1 ∏ k ( p i p i ) c i where ∑ c i = 0 .
For this problem since a and b are less than 1 0 0 only possible values for b a are b a = 3 3 2 2 , 2 2 3 3 Now if b a is a solution to the equation † then m b m a is a solution too. So the solutions are ( 2 2 , 3 3 ) , ( 2 3 , 2 × 3 3 ) , ( 3 × 2 2 , 3 4 ) , ( 3 3 , 2 2 ) , ( 2 × 3 3 , 2 3 ) , ( 3 4 , 3 × 2 2 )