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%I #20 Jan 21 2022 05:08:03
%S 1,2,3,4,8,12,16,32,48,64,128,192,256,512,768,1024,2048,3072,4096,
%T 8192,12288,16384,32768,49152,65536,131072,196608,262144,524288,
%U 786432,1048576,2097152,3145728,4194304,8388608,12582912,16777216,33554432
%N a(3n)=4^n, a(3n+1)=2*4^n, a(3n+2)=3*4^n.
%H <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (0,0,4).
%F O.g.f.: -(1+2*x+3*x^2)/(-1+4*x^3) . 2*a(n)-a(n+1) = abs(A117902(n+1)). - _R. J. Mathar_, Nov 30 2007
%F From _Reinhard Zumkeller_, May 26 2008: (Start)
%F a(n+1) = a(n) + a(n - n mod 3).
%F a(n) = A140740(n+3,3). (End)
%F Sum_{n>=0} 1/a(n) = 22/9. - _Amiram Eldar_, Jan 21 2022
%t LinearRecurrence[{0,0,4},{1,2,3},40] (* _Harvey P. Dale_, Jun 07 2012 *)
%o (PARI) a(n)=4^(n\3)*(n%3+1) \\ _Charles R Greathouse IV_, Oct 07 2015
%Y Cf. A000079, A037124, A038754, A140730, A140740.
%K nonn,easy
%O 0,2
%A _Paul Curtz_, Nov 28 2007
%E Edited by _R. J. Mathar_, Nov 30 2007
%E More terms from _Reinhard Zumkeller_, May 26 2008
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