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a(n)=(s(n)+1)/4, where s(n)=n-th base 4 palindrome that starts with 3.
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%I #5 Jul 12 2012 00:39:46

%S 1,4,13,14,15,16,49,54,59,64,193,197,201,205,210,214,218,222,227,231,

%T 235,239,244,248,252,256,769,789,809,829,834,854,874,894,899,919,939,

%U 959,964,984,1004,1024,3073,3089,3105,3121,3141

%N a(n)=(s(n)+1)/4, where s(n)=n-th base 4 palindrome that starts with 3.

%K nonn,base

%O 1,2

%A _Clark Kimberling_