1/3 the number of n X n 0..2 symmetric matrices with every element equal to zero, one, two or four horizontal and vertical neighbors.
A211048
1/3 the number of n X n 0..2 symmetric matrices with every element equal to zero, one, two or four horizontal and vertical neighbors.
Terms
- a(0) =1a(1) =9a(2) =226a(3) =15556a(4) =2941772a(5) =1527584784
External references
- oeis: A211048