Number of (n+1) X (n+1) -5..5 symmetric matrices with every 2 X 2 subblock having sum zero and one or three distinct values.

A211331

Number of (n+1) X (n+1) -5..5 symmetric matrices with every 2 X 2 subblock having sum zero and one or three distinct values.

Terms

    a(0) =47a(1) =99a(2) =201a(3) =397a(4) =789a(5) =1531a(6) =2999a(7) =5801a(8) =11307a(9) =21927a(10) =42763a(11) =83311a(12) =162977a(13) =319089a(14) =626611a(15) =1232377a(16) =2429037a(17) =4795401a(18) =9482053a(19) =18776315a(20) =37223555a(21) =73884069a(22) =146773655a(23) =291853839a(24) =580697115a(25) =1156276783a(26) =2303407301a(27) =4591264605

External references