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a(n)=2a(n-1)+3a(n-2)+2a(n-3)+3a(n-4).
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%I #13 Jun 13 2015 00:48:56

%S 2,6,19,61,197,633,2036,6548,21061,67737,217861,700699,2253638,

%T 7248306,23312507,74979305,241153657,775615161,2494587424,8023265560,

%U 25804984685,82995786381,266936820209,858540765611

%N a(n)=2a(n-1)+3a(n-2)+2a(n-3)+3a(n-4).

%H Harvey P. Dale, <a href="/A022015/b022015.txt">Table of n, a(n) for n = 0..1000</a>

%H <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (2,3,2,3).

%F G.f.: -(((1+x)*(2+x^2))/(-1+x(2+3*x)*(1+x^2))). - _Harvey P. Dale_, May 04 2015

%t LinearRecurrence[{2,3,2,3},{2,6,19,61},30] (* _Harvey P. Dale_, May 04 2015 *)

%K nonn

%O 0,1

%A _R. K. Guy_