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ILL 1984 Problem 22

    In a permutation (x1,x2,…,xn)(x_1, x_2, \dots , x_n) of the set 1,2,…,n1, 2, \dots , n we call a pair (xi,xj)(x_i, x_j ) discordant if i<ji < j and xi>xjx_i > x_j. Let d(n,k)d(n, k) be the number of such permutations with exactly kk discordant pairs. Find d(n,2)d(n, 2) and d(n,3).d(n, 3).

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