a(n) = T(7,n), array T given by A048471.

Terms

a(0) =1a(1) =129a(2) =513a(3) =1665a(4) =5121a(5) =15489a(6) =46593a(7) =139905a(8) =419841a(9) =1259649a(10) =3779073a(11) =11337345a(12) =34012161a(13) =102036609a(14) =306109953a(15) =918329985a(16) =2754990081a(17) =8264970369a(18) =24794911233a(19) =74384733825a(20) =223154201601a(21) =669462604929