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%I #19 Apr 20 2024 10:27:25
%S 5,51,455,3855,31775,258111,2080895,16711935,133956095,1072694271,
%T 8585742335,68702703615,549688713215,4397778092031,35183298379775,
%U 281470681808895,2251782633947135,18014329790267391,144114913198473215,1152920405096267775,9223367638810361855
%N Numbers whose binary representation is the concatenation of n 1's, n 0's and n 1's.
%C Numbers whose binary representation are the members of A138721.
%H <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (15,-70,120,-64).
%F G.f.: x*(40*x^2-24*x+5)/((x-1)*(2*x-1)*(4*x-1)*(8*x-1)). - _Colin Barker_, Nov 04 2012
%F a(n) = (2^n-1)*(2^(2*n)+1) = 8^n - 4^n + 2^n - 1. - _Alois P. Heinz_, Nov 04 2012
%p a:= n-> 8^n-4^n+2^n-1:
%p seq(a(n), n=1..30); # _Alois P. Heinz_, Nov 04 2012
%Y Cf. A138721.
%K easy,nonn,base,changed
%O 1,1
%A _Omar E. Pol_, Oct 14 2008
%E More terms from _Colin Barker_, Nov 04 2012
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