Fermat's little theorem


p is a prime number and {a} can't be divided by p.

You use the strong induction to prove Fermat's little theorem.



This is the 7th row of Pascal’s triangle.


Odd numbers are 1, and even numbers are 0.


This is fractal.


i


0

1

2

3

4

5

6

7

p


1

7

21

35

35

21

7

1



(p,i)≡0 mod p


(i≠0,7)


For example, (7,2)=7!/2!(7-2)!=5040/240=21

p!=p(p-1)!



1^p≡1 mod p


This is apparent.

Therefore

2^p=(1+1)^p=1+(p,1)+(p,2)+・・・+(p,p-1)+1≡1+0+0+0+・・・+1=2 mod p

3^p=(1+2)^p=1+2(p,1)+2^2(p,2)+・・・+2^(p-1)(p,p-1)+2^p≡1+0+0+0+・・・+2=3 mod p

4^p=(1+3)^p=1+3(p,1)+3^2(p,2)+・・・+3^(p-1)(p,p-1)+3^p≡1+0+0+0+・・・+3=4 mod p

You can expand it because of Pascal’s triangle which is the binomial theorem.


(n,i)=n!/i!(n-i)!


Then you define a^(p-1).

5^16≡1 mod 17

This is also clear, so you can prove the strong induction.













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