a(n)=(s(n)+2)/7, where s(n)=n-th base 7 palindrome that starts with 5.

Terms

a(0) =1a(1) =6a(2) =36a(3) =37a(4) =38a(5) =39a(6) =40a(7) =41a(8) =42a(9) =246a(10) =254a(11) =262a(12) =270a(13) =278a(14) =286a(15) =294a(16) =1716a(17) =1723a(18) =1730a(19) =1737a(20) =1744a(21) =1751a(22) =1758a(23) =1766a(24) =1773a(25) =1780a(26) =1787a(27) =1794a(28) =1801a(29) =1808