92741domain: NAppears in sequencesNumber of (n+1) X (n+1) -3..3 symmetric matrices with every 2 X 2 subblock having sum zero and one or two distinct values.at n=20A211322Dirichlet g.f.: Product_{k>=2} 1 / (1 - k^(-s))^binomial(k+3,4).at n=31A344204