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%I #15 May 09 2024 04:44:31
%S 4,1,16,4,64,16,256,64,1024,256,4096,1024,16384,4096,65536,16384,
%T 262144,65536,1048576,262144,4194304,1048576,16777216,4194304,
%U 67108864,16777216,268435456,67108864,1073741824,268435456,4294967296,1073741824
%N Pair-reversal of 1,4,4,16,16...
%H <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (0,4).
%F a(n) = k^(n/2)(1+k*sqrt(k)-(1-ksqrt(k))(-1)^n)/(2*sqrt(k)), the pair reversal of 1,k,k,k^2,k^2,k^3,k^3,... for k=4.
%F G.f.: (4+x)/(1-4*x^2).
%F a(n) = (9*2^n+7*(-2)^n)/4.
%F Recurrence: a(n) = 4a(n-2), a(0)=4, a(1)=1. - _Ralf Stephan_, Jul 17 2013
%t LinearRecurrence[{0,4},{4,1},50] (* _Harvey P. Dale_, Apr 15 2017 *)
%Y Cf. A076736.
%K nonn,easy
%O 0,1
%A _Paul Barry_, Apr 26 2004