Number of (n+1)X(n+1) -9..9 symmetric matrices with every 2X2 subblock having sum zero and one, two or three distinct values.
A211553
Number of (n+1)X(n+1) -9..9 symmetric matrices with every 2X2 subblock having sum zero and one, two or three distinct values.
Terms
- a(0) =181a(1) =521a(2) =1239a(3) =2865a(4) =6321a(5) =14009a(6) =30379a(7) =66865a(8) =145437a(9) =322009a(10) =708509a(11) =1586445a(12) =3542267a(13) =8034795a(14) =18210199a(15) =41826241a(16) =96089585a(17) =223154883a(18) =518575357a(19) =1215390177a(20) =2850562247a(21) =6729628421a(22) =15897536413a(23) =37742249421a(24) =89649505903
External references
- oeis: A211553