3860558314domain: NAppears in sequencesa(n) = Sum_{i=1..n} (Product_{j=1..n} M(j, ((i+j-2) mod n)+1) + Product_{j=1..n} M(j, ((i-j-1) mod n)+1)) where M is an n X n Toeplitz matrix whose first row consists of successive positive integer numbers 1, ..., n and whose first column consists of 1, n + 1, ..., 2*n - 1.at n=9A389504