Problem : Find number of co-primes pair (x,y,z) in a list of numbers.

My solution:

No of (even, odd, odd) + No of (even,even,odd) + No of (odd,odd,odd).

lets say N is number of even and M is no of odd.

(even, even, odd) = (N!/2!(N-2)!) * M

(even, odd, odd) = N*(M!/2!(M-2)!)

and for (odd,odd,odd) I dont know how to get because of following

( x belong to set M, y belong to set k(x), z belong to set (M-2) (excluding x and y))

(note: k(x) is a subset of M)

k(x) = list of numbers not divisible by x

How to find the number of combinations to pick 3 numbers.

Sorry I don't know how to use mathematical symbols in the question.


  • $\begingroup$ What does "set (N-1)" mean? $\endgroup$ – barak manos Jun 29 '14 at 7:00
  • $\begingroup$ set N excluding x $\endgroup$ – Sab Jun 29 '14 at 8:23
  • $\begingroup$ I don't have an answer, but as far as symbols are concerned, see math notation guide. $\endgroup$ – user147263 Aug 13 '14 at 19:47

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Browse other questions tagged or ask your own question.