a(n) = floor(7^n/3^n).

Terms

a(0) =1a(1) =2a(2) =5a(3) =12a(4) =29a(5) =69a(6) =161a(7) =376a(8) =878a(9) =2050a(10) =4783a(11) =11162a(12) =26044a(13) =60771a(14) =141799a(15) =330865a(16) =772020a(17) =1801380a(18) =4203220a(19) =9807513a(20) =22884198a(21) =53396463a(22) =124591747a(23) =290714077a(24) =678332846a(25) =1582776641a(26) =3693145496a(27) =8617339492a(28) =20107125483a(29) =46916626127