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%I #10 Sep 08 2022 08:45:49
%S 6,21,69,219,681,2091,6369,19299,58281,175611,528369,1588179,4770681,
%T 14324331,42997569,129041859,387223881,1161868251,3485997969,
%U 10458780339,31377913881,94136887371,282416953569,847263443619,2541815496681,7625496821691,22876591128369
%N a(n) = 3^n - 3*2^(n-2).
%H Vincenzo Librandi, <a href="/A169687/b169687.txt">Table of n, a(n) for n = 2..1000</a>
%o (Magma) [3^n-3*2^(n-2): n in [2..35]]; // _Vincenzo Librandi_, Jun 30 2011
%Y Arises in the analysis of A169688.
%K nonn,easy
%O 2,1
%A _N. J. A. Sloane_, Apr 14 2010
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