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a(n) = (s(n)+1)/3, where s(n) = n-th base 3 palindrome that starts with 2.
1

%I #7 Apr 30 2022 21:25:33

%S 1,3,7,8,9,19,23,27,55,58,61,65,68,71,75,78,81,163,175,187,191,203,

%T 215,219,231,243,487,496,505,517,526,535,547,556,565,569,578,587,599,

%U 608,617,629,638,647,651,660,669,681,690,699,711

%N a(n) = (s(n)+1)/3, where s(n) = n-th base 3 palindrome that starts with 2.

%K nonn,base

%O 1,2

%A _Clark Kimberling_