a(n)=(s(n)+3)/7, where s(n)=n-th base 7 palindrome that starts with 4.

Terms

a(0) =1a(1) =5a(2) =29a(3) =30a(4) =31a(5) =32a(6) =33a(7) =34a(8) =35a(9) =197a(10) =205a(11) =213a(12) =221a(13) =229a(14) =237a(15) =245a(16) =1373a(17) =1380a(18) =1387a(19) =1394a(20) =1401a(21) =1408a(22) =1415a(23) =1423a(24) =1430a(25) =1437a(26) =1444a(27) =1451a(28) =1458a(29) =1465