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

A211713

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

Terms

    a(0) =264a(1) =726a(2) =1670a(3) =3574a(4) =7448a(5) =15136a(6) =30436a(7) =60938a(8) =120832a(9) =241150a(10) =476020a(11) =951586a(12) =1878928a(13) =3771022a(14) =7467440a(15) =15063942a(16) =29958046a(17) =60772582a(18) =121463624a(19) =247803532a(20) =497864910a(21) =1021347926a(22) =2062591634a(23) =4253485786a(24) =8631871242a(25) =17886996814

External references