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FORMULE , ALEA ALEA

comb(n,k)=n!/k!(n-k)! 
perm(n)=n!
aranj(n,k)=n!/(n-k)!


A(n,k)=C(n,k)*P(k) - P(k)=k!

               k
notatie comb: C          - combinari de n luate cate k - comb(n,k)
               n  

* (n,k) - n luate cate k 

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Nr. lui Catalan: - numarul de parantezari
Nr. CAT= (1/n+1)*C(n,2n) = (1/n+1)*(2n!/(n!*n!))

Calculare CATALAN pe numere mari (invers modular)
- de completat: http://infoarena.ro/problema/inversmodular

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