wolf
New member
- Joined
- Nov 28, 2013
- Messages
- 29
A derangement is a type of combination where each element is not in its original position.
For example how many ways can 1 2 3 be arranged so that 1 isn't first 2 isn't second and 3 isn't third?
For small values of 'n' it is easy just to list all of them:
2 3 1 and 3 1 2
So when n=3, there are 2 possible derangements.
When n = 4 there are 9 derangements.
There is a formula for calculating derangements:
n! * (1 - 1/1! +1/2! - 1/3! + 1/4! ..... +- 1/n!)
Is there another formula for this?
Thank you.
For example how many ways can 1 2 3 be arranged so that 1 isn't first 2 isn't second and 3 isn't third?
For small values of 'n' it is easy just to list all of them:
2 3 1 and 3 1 2
So when n=3, there are 2 possible derangements.
When n = 4 there are 9 derangements.
There is a formula for calculating derangements:
n! * (1 - 1/1! +1/2! - 1/3! + 1/4! ..... +- 1/n!)
Is there another formula for this?
Thank you.