login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A170877 Number of binary words of length n with properties that there is no pair of adjacent 1's and no subword of the form X^4 for any string X. 1
1, 2, 3, 5, 7, 10, 15, 22, 30, 43, 61, 88, 123, 173, 246, 348, 487, 688, 972, 1371, 1928, 2714, 3822, 5387, 7582, 10681, 15046, 21194, 29835, 42009, 59159, 83305, 117292, 165170, 232593, 327530, 461198, 649431, 914493, 1287747, 1813281, 2553346, 3595465 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

The subword 01010101 (corresponding to X = 01) for example cannot occur.

LINKS

Lars Blomberg, Table of n, a(n) for n = 0..43

EXAMPLE

a(3) = 5: 000, 001, 010, 100, 101.

a(4) = 7: 0001, 0010, 0100, 1000, 0101, 1010, 1001.

CROSSREFS

Cf. A003410, A028445, A135491.

Sequence in context: A225490 A076972 A301756 * A003410 A018133 A261081

Adjacent sequences:  A170874 A170875 A170876 * A170878 A170879 A170880

KEYWORD

nonn

AUTHOR

Benjamin Chaffin and N. J. A. Sloane, Jan 07 2010

EXTENSIONS

a(24)-a(42) from Lars Blomberg, Aug 22 2013

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified July 31 18:22 EDT 2021. Contains 346376 sequences. (Running on oeis4.)