perplexus.info :: Just Math : Equation with factorial

Equation with factorial (Posted on 2018-10-20)

Solve in integers for x and y: 6(x! + 3) = y^2 + 5

No Solution Yet Submitted by Ady TZIDON

No Rating

Comments: ( Back to comment list | You must be logged in to post comments.)

soln

Comment 1 of 1

x must be less than 5 (it is from choices: 0,1,2,3,4). Why?

x>=5 --> x! is a multiple of 10, and so is 6(x!). The equation:

6(x!)=y^2 -13 means that for x>=5, y^2 must end in 3, which is impossible for integers.

What works is (2,5) and (3,7) and also (2,-5) and (3,-7)

Edited on October 21, 2018, 3:32 am

Posted by Steven Lord on 2018-10-20 11:09:48

Please log in:

Forums (0)
Newest Problems
Random Problem
FAQ | About This Site
Site Statistics
New Comments (0)
Unsolved Problems
Top Rated Problems
This month's top
Most Commented On

Chatterbox:


perplexus dot info