Permutation & Combination
P(n,k), C(n,k), n^k, with-repetition variants and factorial — exact BigInt results.
Enter n (the pool size) and k (how many you pick). Permutation P(n,k) = n!/(n−k)! counts ordered arrangements; Combination C(n,k) = n!/(k!(n−k)!) counts unordered selections; n^k is permutations with repetition; C(n+k−1, k) is combinations with repetition; n! is factorial. All results are computed exactly with BigInt, so they stay correct even for large values (though very big inputs produce very long numbers). P and C are 0 when k exceeds n.