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!)
A089973 Number of maximum-length 2-surprising sequences in n symbols. 1
1, 6, 24, 48, 25440, 554400 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

A sequence of symbols is 2-surprising if, for every pair of symbols X and Y, not necessarily distinct and every distance D, there is at most one position in t he sequence where X precedes Y by distance D. The maximum lengths are given in A008062.

REFERENCES

Dennis E. Shasha, Puzzling Adventures, Scientific American 289(#12, 2003), 22.

LINKS

Table of n, a(n) for n=1..6.

EXAMPLE

The 2-surprising sequences in 3 symbols are:

(2012100) (1021200) (1120210) (2011210) (1202210) (2210120) (2101120) (1022120)

(2100201) (0021201) (0212201) (2102011) (0120211) (2010021) (2201021) (0122021)

(1200102) (0121102) (0012102) (1020012) (0211012) (1102012) (1201022) (0210122)

Thus a(3)=24.

CROSSREFS

Cf. A008062.

Sequence in context: A000056 A083170 A087081 * A277014 A033581 A213393

Adjacent sequences:  A089970 A089971 A089972 * A089974 A089975 A089976

KEYWORD

nonn

AUTHOR

John W. Layman, Nov 17 2003

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 March 3 13:41 EST 2021. Contains 341762 sequences. (Running on oeis4.)