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

0, 1010, 110110, 11101110, 1111011110, 111110111110, 11111101111110, 1111111011111110, 111111110111111110, 11111111101111111110, 1111111111011111111110, 111111111110111111111110

Offset

0,2

Comments

a(n) is also A170940(n+1) written in base 2.

Links

Table of n, a(n) for n=0..11.

Index entries for linear recurrences with constant coefficients, signature (111,-1110,1000).

Formula

G.f.: 10*x*(200*x-101) / ((x-1)*(10*x-1)*(100*x-1)). [Colin Barker, Sep 17 2013]

Example

n ............... a(n)
0 ................ 0
1 ............... 1010
2 .............. 110110
3 ............. 11101110
4 ............ 1111011110
5 ........... 111110111110
6 .......... 11111101111110
7 ......... 1111111011111110
8 ........ 111111110111111110
9 ....... 11111111101111111110

Mathematica

Table[FromDigits[Join[PadRight[{}, n, 1], {0}, PadRight[{}, n, 1], {0}]], {n, 0, 20}] (* Harvey P. Dale, Feb 25 2012 *)

Prog

(PARI) Vec(10*x*(200*x-101)/((x-1)*(10*x-1)*(100*x-1))  + O(x^100)) \\ Colin Barker, Sep 17 2013

Crossrefs

Cf. A138148, A170940.

Sequence in context: A252683 A157010 A076940 * A266442 A266673 A055473

Adjacent sequences: A173518 A173519 A173520 * A173522 A173523 A173524

Keyword

base,easy,nonn

Author

Omar E. Pol, Mar 16 2010

Status

approved