a(n) = 13 + floor(Sum_{j=1..n-1} a(j)/3).

Terms

a(0) =13a(1) =17a(2) =23a(3) =30a(4) =40a(5) =54a(6) =72a(7) =96a(8) =128a(9) =170a(10) =227a(11) =303a(12) =404a(13) =538a(14) =718a(15) =957a(16) =1276a(17) =1701a(18) =2268a(19) =3024a(20) =4032a(21) =5376a(22) =7168a(23) =9558a(24) =12744a(25) =16992a(26) =22656a(27) =30208a(28) =40277a(29) =53703