Determine the number of binary relations on a set $A = {a_1, a_2, . . . , a_n}$ containing for each pair of distinct elements $a_i, a_j$ exactly one of the ordered pairs $(a_i, a_j)$ and $(a_j , a_i)$
Determine the number of binary relations on a set $A = {a_1, a_2, . . . , a_n}$
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combinatorics
discrete-mathematics