a(n) = Sum_{k >= 1} floor(2*tau^(n-k)).

Terms

a(0) =3a(1) =6a(2) =11a(3) =19a(4) =32a(5) =54a(6) =89a(7) =147a(8) =240a(9) =392a(10) =637a(11) =1035a(12) =1678a(13) =2720a(14) =4405a(15) =7133a(16) =11546a(17) =18688a(18) =30243a(19) =48941a(20) =79194a(21) =128146a(22) =207351a(23) =335509a(24) =542872a(25) =878394a(26) =1421279a(27) =2299687a(28) =3720980a(29) =6020682