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

A210820

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