a(n) = T(7,n), array T given by A048472.

Terms

a(0) =1a(1) =9a(2) =33a(3) =97a(4) =257a(5) =641a(6) =1537a(7) =3585a(8) =8193a(9) =18433a(10) =40961a(11) =90113a(12) =196609a(13) =425985a(14) =917505a(15) =1966081a(16) =4194305a(17) =8912897a(18) =18874369a(19) =39845889a(20) =83886081a(21) =176160769a(22) =369098753a(23) =771751937a(24) =1610612737a(25) =3355443201a(26) =6979321857a(27) =14495514625a(28) =30064771073a(29) =62277025793