10601986domain: NAppears in sequencesHalf the number of n X n binary matrices, symmetric under horizontal reflection, having equal row sums.at n=8A140217a(n) = Sum_{k = 0..n} C(n,k)^9.at n=4A182446a(n) is the sum of the n-th powers of the terms of row 4 of Pascal's triangle.at n=9A363299