Partial sums of round(3^n/7).

Terms

a(0) =0a(1) =0a(2) =1a(3) =5a(4) =17a(5) =52a(6) =156a(7) =468a(8) =1405a(9) =4217a(10) =12653a(11) =37960a(12) =113880a(13) =341640a(14) =1024921a(15) =3074765a(16) =9224297a(17) =27672892a(18) =83018676a(19) =249056028a(20) =747168085a(21) =2241504257a(22) =6724512773a(23) =20173538320a(24) =60520614960a(25) =181561844880