Number of (n+1)X(n+1) -11..11 symmetric matrices with every 2X2 subblock having sum zero and one or three distinct values.

A211712

Number of (n+1)X(n+1) -11..11 symmetric matrices with every 2X2 subblock having sum zero and one or three distinct values.

Terms

    a(0) =231a(1) =537a(2) =1099a(3) =2099a(4) =3997a(5) =7379a(6) =13747a(7) =25335a(8) =47093a(9) =87513a(10) =163699a(11) =307721a(12) =581223a(13) =1105495a(14) =2109715a(15) =4055319a(16) =7812709a(17) =15150193a(18) =29420803a(19) =57448799a(20) =112272663a(21) =220389539a(22) =432816337a(23) =852950837a(24) =1681246791a(25) =3322791067

External references