Number of different n X n symmetric matrices with nonnegative entries summing to 4. Also number of symmetric oriented graphs with 4 arcs on n points.

A139594

Number of different n X n symmetric matrices with nonnegative entries summing to 4. Also number of symmetric oriented graphs with 4 arcs on n points.

Terms

    a(0) =0a(1) =1a(2) =9a(3) =39a(4) =116a(5) =275a(6) =561a(7) =1029a(8) =1744a(9) =2781a(10) =4225a(11) =6171a(12) =8724a(13) =11999a(14) =16121a(15) =21225a(16) =27456a(17) =34969a(18) =43929a(19) =54511a(20) =66900a(21) =81291a(22) =97889a(23) =116909a(24) =138576a(25) =163125a(26) =190801a(27) =221859a(28) =256564a(29) =295191

External references