1/3 the number of n X n 0..2 symmetric matrices with every element equal to zero, one or two horizontal and vertical neighbors.
A211039
1/3 the number of n X n 0..2 symmetric matrices with every element equal to zero, one or two horizontal and vertical neighbors.
Terms
- a(0) =1a(1) =9a(2) =204a(3) =12780a(4) =2172082a(5) =1005151346
External references
- oeis: A211039