a(n) = (a(n-1) - a(n-3))*7^((1+(-1)^n)/2) with a(6)=5, a(7)=4, a(8)=22.

Terms

a(0) =5a(1) =4a(2) =22a(3) =17a(4) =91a(5) =69a(6) =364a(7) =273a(8) =1428a(9) =1064a(10) =5537a(11) =4109a(12) =21315a(13) =15778a(14) =81683a(15) =60368a(16) =312130a(17) =230447a(18) =1190553a(19) =878423a(20) =4535832a(21) =3345279a(22) =17267992a(23) =12732160a(24) =65708167a(25) =48440175a(26) =249956105a(27) =184247938a(28) =950654341a(29) =700698236