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%I #17 Apr 20 2024 10:23:08
%S 0,1010,110110,11101110,1111011110,111110111110,11111101111110,
%T 1111111011111110,111111110111111110,11111111101111111110,
%U 1111111111011111111110,111111111110111111111110
%N a(n) is the concatenation of n 1's, 0, n 1's and 0.
%C a(n) is also A170940(n+1) written in base 2.
%H <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (111,-1110,1000).
%F G.f.: 10*x*(200*x-101) / ((x-1)*(10*x-1)*(100*x-1)). [_Colin Barker_, Sep 17 2013]
%e n ............... a(n)
%e 0 ................ 0
%e 1 ............... 1010
%e 2 .............. 110110
%e 3 ............. 11101110
%e 4 ............ 1111011110
%e 5 ........... 111110111110
%e 6 .......... 11111101111110
%e 7 ......... 1111111011111110
%e 8 ........ 111111110111111110
%e 9 ....... 11111111101111111110
%t Table[FromDigits[Join[PadRight[{},n,1],{0},PadRight[{},n,1],{0}]],{n,0,20}] (* _Harvey P. Dale_, Feb 25 2012 *)
%o (PARI) Vec(10*x*(200*x-101)/((x-1)*(10*x-1)*(100*x-1)) + O(x^100)) \\ _Colin Barker_, Sep 17 2013
%Y Cf. A138148, A170940.
%K base,easy,nonn
%O 0,2
%A _Omar E. Pol_, Mar 16 2010