a(n) = Sum_{k divides 3^n} S(k), where S is the Kempner function A002034.

Terms

a(0) =1a(1) =4a(2) =10a(3) =19a(4) =28a(5) =40a(6) =55a(7) =73a(8) =91a(9) =112a(10) =136a(11) =163a(12) =190a(13) =217a(14) =247a(15) =280a(16) =316a(17) =352a(18) =391a(19) =433a(20) =478a(21) =523a(22) =571a(23) =622a(24) =676a(25) =730a(26) =784a(27) =841a(28) =901a(29) =964