a(n) = floor( Gamma(n+4/7)/Gamma(4/7) ).

Terms

a(0) =1a(1) =0a(2) =0a(3) =2a(4) =8a(5) =37a(6) =210a(7) =1380a(8) =10450a(9) =89574a(10) =857351a(11) =9063434a(12) =104876887a(13) =1318452295a(14) =17893281147a(15) =260730668150