Partial sums of floor(4^n/7).

Terms

a(0) =0a(1) =2a(2) =11a(3) =47a(4) =193a(5) =778a(6) =3118a(7) =12480a(8) =49929a(9) =199725a(10) =798911a(11) =3195656a(12) =12782636a(13) =51130558a(14) =204522247a(15) =818089003a(16) =3272356029a(17) =13089424134a(18) =52357696554a(19) =209430786236a(20) =837723144965