1/4 the number of n X n 0..3 symmetric matrices with every element equal to zero, one, three or four horizontal and vertical neighbors.
A211091
1/4 the number of n X n 0..3 symmetric matrices with every element equal to zero, one, three or four horizontal and vertical neighbors.
Terms
- a(0) =1a(1) =9a(2) =324a(3) =36801a(4) =13804290a(5) =17121995676
External references
- oeis: A211091