Let B be a nonempty and proper subset of A_n = {1,2,...,p_n-1}, where p_n is the n-th prime. Let C be the complement of B, so that the union B and C is A_n. a(n) is half the number of sums of products of elements of B and elements of C which are divisible by p_n, when B runs through all such subsets of A_n.

A238446

Let B be a nonempty and proper subset of A_n = {1,2,...,p_n-1}, where p_n is the n-th prime. Let C be the complement of B, so that the union B and C is A_n. a(n) is half the number of sums of products of elements of B and elements of C which are divisible by p_n, when B runs through all such subsets of A_n.