1/4 the number of n X n 0..3 symmetric matrices with every element equal to one or two horizontal and vertical neighbors.
A211080
1/4 the number of n X n 0..3 symmetric matrices with every element equal to one or two horizontal and vertical neighbors.
Terms
- a(0) =0a(1) =1a(2) =6a(3) =276a(4) =19788a(5) =4909014a(6) =2929172742
External references
- oeis: A211080