Number of (n+1)X(n+1) -9..9 symmetric matrices with every 2X2 subblock having sum zero and two, three or four distinct values.
A211556
Number of (n+1)X(n+1) -9..9 symmetric matrices with every 2X2 subblock having sum zero and two, three or four distinct values.
Terms
- a(0) =180a(1) =1712a(2) =16318a(3) =155904a(4) =1492928a(5) =14327826a(6) =137797604a(7) =1327935624a(8) =12821402190a(9) =124011705656
External references
- oeis: A211556