cp's OEIS Frontend

A173521 a(n) is the concatenation of n 1's, 0, n 1's and 0.

%I A173521 #17 Apr 20 2024 10:23:08
%S A173521 0,1010,110110,11101110,1111011110,111110111110,11111101111110,
%T A173521 1111111011111110,111111110111111110,11111111101111111110,
%U A173521 1111111111011111111110,111111111110111111111110
%N A173521 a(n) is the concatenation of n 1's, 0, n 1's and 0.
%C A173521 a(n) is also A170940(n+1) written in base 2.
%H A173521 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (111,-1110,1000).
%F A173521 G.f.: 10*x*(200*x-101) / ((x-1)*(10*x-1)*(100*x-1)). [_Colin Barker_, Sep 17 2013]
%e A173521 n ............... a(n)
%e A173521 0 ................ 0
%e A173521 1 ............... 1010
%e A173521 2 .............. 110110
%e A173521 3 ............. 11101110
%e A173521 4 ............ 1111011110
%e A173521 5 ........... 111110111110
%e A173521 6 .......... 11111101111110
%e A173521 7 ......... 1111111011111110
%e A173521 8 ........ 111111110111111110
%e A173521 9 ....... 11111111101111111110
%t A173521 Table[FromDigits[Join[PadRight[{},n,1],{0},PadRight[{},n,1],{0}]],{n,0,20}] (* _Harvey P. Dale_, Feb 25 2012 *)
%o A173521 (PARI) Vec(10*x*(200*x-101)/((x-1)*(10*x-1)*(100*x-1))  + O(x^100)) \\ _Colin Barker_, Sep 17 2013
%Y A173521 Cf. A138148, A170940.
%K A173521 base,easy,nonn
%O A173521 0,2
%A A173521 _Omar E. Pol_, Mar 16 2010