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

A210815

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