Factorial Q: How to Get (n+1)!

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SUMMARY

The factorial of (n + 1) is defined as (n + 1)! = (n + 1) * n!. This can be derived from the recursive relationship of factorials, where (n + 1)! is expressed as (n + 1) multiplied by the factorial of n, which is n!. The confusion often arises from the notation, but understanding that (n + 1 - k) simplifies to n - k for k = 1, 2, 3, ... clarifies the relationship.

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askor
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How do you get

(n + 1)! = (n + 1)(n)(n - 1)(n - 2) ... 3 ⋅ 2 ⋅ 1

?

Isn't (n + 1)! = (n + 1) ⋅ (n + 1 - 1) ⋅ (n + 1 - 2) ⋅ (n + 1 - 3) ⋅ (n + 1 - 4) ... and so on?
 
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askor said:
How do you get

(n + 1)! = (n + 1)(n)(n - 1)(n - 2) ... 3 ⋅ 2 ⋅ 1

?

Isn't (n + 1)! = (n + 1) ⋅ (n + 1 - 1) ⋅ (n + 1 - 2) ⋅ (n + 1 - 3) ⋅ (n + 1 - 4) ... and so on?
You need to realize that:
n+1-1 = n
n+1-2 = n-1
n+1-3 = n-2
etc
 
or more compactly:

(n+1)! = (n+1) * (n+1-1)! = (n+1) * n!
 

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