Elemente de combinatorica - exemple

Permutari P(n)=1*2*...*n=n!
1 2 3
12
13
21
23
31
32

Aranjamente A(n,k)
A(n,k)= n!/(n-k)!

A(n,0)=1 {}
A(3,1)
1
2
3

C(n,k)=n!/(k!*(n-k)!)




inv= inv*10+c


1234567

7	0+7*1
5 7     7 + 5*10=57
3 57    57 + 3*100=357
1 357   357 + 1*1000=1357

1357=1*10^3 + 3*10^2 + 5 *10^1 + 7* 10^0
3210

nr = nr + c*p



1*2*...    *10
______________
1*2*...*7

m+1*...*n