(9*7^n+1)/2.

Terms

a(0) =5a(1) =32a(2) =221a(3) =1544a(4) =10805a(5) =75632a(6) =529421a(7) =3705944a(8) =25941605a(9) =181591232a(10) =1271138621a(11) =8897970344a(12) =62285792405a(13) =436000546832