Combinatorics

Permutations (k)
A(k, n) = n! / (n - k)!
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Permutations
P(n) = n!
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Combinations
C(k, n) = n! / k! /(n - k)!
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Combinations and permutations
A(n, k) = k! * C(k, n)
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Binomial Theorem
T(k+1) = C(k, n) * a^(n-k) * b^k
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