cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

Showing 1-5 of 5 results.

A000983 Size of minimal binary covering code of length n and covering radius 1.

Original entry on oeis.org

1, 2, 2, 4, 7, 12, 16, 32, 62
Offset: 1

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Author

Keywords

Comments

For k > 0, a(2^k-1) = 2^(2^k-k-1). In this case the minimal covering code is also a Hamming code.
In the game described in the Wikipedia link, with n players, the optimal strategy wins with probability 1-a(n)/2^n. In the optimal strategy, the players first agree on a minimal covering code of length n. After the hats are placed, each player knows two words of length n such that one of them is the hat colors of the n players. If one of these two words is a member of the covering code and the other word is not, that player guesses the word that is not. Otherwise, that player does not guess. This strategy guarantees that the team wins for all words that are not members of the covering code.
Because each codeword covers n+1 of the 2^n words, A053637(n+1) is a lower bound. - Rob Pratt, Jan 05 2015
a(n) is also the domination number of the n-hypercube graph Q_n. - Eric W. Weisstein, Feb 20 2016
The next term a(10) is in the range 107-120. - Andrey Zabolotskiy, Sep 01 2016

References

  • G. D. Cohen et al., Covering Codes, North-Holland, 1997, p. 166.
  • I. S. Honkala and Patric R. J. Östergård, Code design, Chapter 13 of Local Search in Combinatorial Optimization, E. Aarts and J. K. Lenstra (editors), Wiley, New York 1997, pp. 441-456.
  • N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
  • N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Crossrefs

A column of A060438. Cf. A029866.

A029866 Size of minimal binary covering code of length n and covering radius 2.

Original entry on oeis.org

1, 2, 2, 2, 4, 7, 12, 16
Offset: 2

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Author

Keywords

Comments

Also the domination number of the (n+1)-halved cube graph. - Eric W. Weisstein, Aug 31 2016 and Jul 17 2017 (after discussion with Stan Wagon)

References

  • G. D. Cohen et al., Covering Codes, North-Holland, 1997, p. 166.

Crossrefs

A column of A060438.
Cf. A000983 (domination number of the n-hypercube graph Q_n).

Extensions

a(9) from Andrey Zabolotskiy, Sep 01 2016

A060439 Triangle T(n,k), 1 <= k <= n, giving maximal size of ternary code of length n and covering radius k.

Original entry on oeis.org

1, 3, 1, 5, 3, 1, 9, 3, 3, 1, 27, 8, 3, 3, 1
Offset: 1

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Author

N. J. A. Sloane, Apr 07 2001

Keywords

Comments

Next term, T(6,1), is in range 71-73. - Kamiel P.F. Verstraten, Jun 29 2015

Examples

			Triangle starts:
1;
3,1;
5,3,1;
9,3,3,1;
...
		

References

  • G. D. Cohen et al., Covering Codes, North-Holland, 1997, p. 174.

Crossrefs

First column gives A004044. Cf. A060438, A060440.

A060440 Triangle T(n,k), 1 <= k <= n, giving maximal size of code of length n and covering radius k over alphabet of size 4.

Original entry on oeis.org

1, 4, 1, 8, 4, 1, 24, 7, 4, 1, 64, 16, 4, 4, 1
Offset: 1

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Author

N. J. A. Sloane, Apr 07 2001

Keywords

Examples

			1; 4,1; 8,4,1; 24,7,4,1; ...
		

References

  • G. D. Cohen et al., Covering Codes, North-Holland, 1997, p. 174.

Crossrefs

Extensions

T(5,2)-T(5,5) from Andrey Zabolotskiy, Apr 11 2017 using Gerzson Kéri's tables.

A230014 Triangle E(n,k), 1<=k<=n, giving the cardinality of optimal binary covering codes of empty spheres of length n and radius k.

Original entry on oeis.org

2, 2, 4, 4, 4, 8, 4, 4, 4, 16, 8, 6, 6, 8, 32, 14, 8, 6, 8, 14, 64, 24, 8, 8, 8, 8, 24, 128, 32, 16, 8, 8, 8, 16, 32, 256, 64, 24, 12, 10, 10, 12, 24, 64, 512, 124
Offset: 1

Views

Author

Kamiel P.F. Verstraten, Feb 22 2014

Keywords

Comments

The next term is in the range 34-40.
Note that E(n,k) = E(n,n-k).

Examples

			Triangle starts:
01: 2,
02: 2, 4,
03: 4, 4, 8,
04: 4, 4, 4, 16,
05: 8, 6, 6, 8, 32,
06: 14, 8, 6, 8, 14, 64,
07: 24, 8, 8, 8, 8, 24, 128,
08: 32, 16, 8, 8, 8, 16, 32, 256,
09: 64, 24, 12, 10, 10, 12, 24, 64, 512,
10: 124, ...
		

Crossrefs

Related to A060438, which has a code consisting of filled spheres instead of empty spheres.
Related to A238305, the triangle giving the cardinality of optimal ternary covering codes of empty spheres.
The first column is equal to 2*A000983.

Extensions

a(43) corrected by Omar E. Pol, Nov 23 2014
Showing 1-5 of 5 results.