Number of (n+1)X(n+1) 0..3 symmetric matrices with every 2X2 subblock having two distinct values, and new values 0..3 introduced in lower triangle row major order.

A210827

Number of (n+1)X(n+1) 0..3 symmetric matrices with every 2X2 subblock having two distinct values, and new values 0..3 introduced in lower triangle row major order.