A043060 a(n)=(s(n)+5)/7, where s(n)=n-th base 7 palindrome that starts with 2.
1, 3, 15, 16, 17, 18, 19, 20, 21, 99, 107, 115, 123, 131, 139, 147, 687, 694, 701, 708, 715, 722, 729, 737, 744, 751, 758, 765, 772, 779, 787, 794, 801, 808, 815, 822, 829, 837, 844, 851, 858, 865, 872, 879, 887, 894, 901, 908
Offset: 1