Number of (n+1)X(n+1) -9..9 symmetric matrices with every 2X2 subblock having sum zero and three distinct values.
A211550
Number of (n+1)X(n+1) -9..9 symmetric matrices with every 2X2 subblock having sum zero and three distinct values.
Terms
- a(0) =150a(1) =330a(2) =640a(3) =1190a(4) =2172a(5) =3922a(6) =7052a(7) =12734a(8) =22944a(9) =41816a(10) =76046a(11) =140318a(12) =258302a(13) =482748a(14) =900018a(15) =1702150a(16) =3211388a(17) =6136202a(18) =11697780a(19) =22541648a(20) =43345282a(21) =84091266a(22) =162828522a(23) =317556046a(24) =618284124a(25) =1210700090a(26) =2367405022a(27) =4650241676
External references
- oeis: A211550