a(n) = Sum_{k=0..3^(n-1)} gcd(k,3^(n-1)) for n > 0 and a(0) = 1.

Terms

a(0) =1a(1) =2a(2) =8a(3) =30a(4) =108a(5) =378a(6) =1296a(7) =4374a(8) =14580a(9) =48114a(10) =157464a(11) =511758a(12) =1653372a(13) =5314410a(14) =17006112a(15) =54206982a(16) =172186884a(17) =545258466a(18) =1721868840a(19) =5423886846a(20) =17046501516a(21) =53464027482a(22) =167365651248a(23) =523017660150