The On-Line Encyclopedia of Integer Sequences (OEIS)

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A081000

n is a member if and only if it ranks among top n positive integers in centrality (cf. A080997 for fuller description of this concept).
(history; published version)

#5 by Russ Cox at Fri Mar 30 17:27:18 EDT 2012

AUTHOR

_Matthew Vandermast (ghodges14(AT)comcast.net), _, Mar 02 2003

Discussion

Fri Mar 30

17:27

OEIS Server: https://oeis.org/edit/global/142

#4 by N. J. A. Sloane at Sun Feb 20 03:00:00 EST 2005

KEYWORD

nonn,new

nonn

AUTHOR

Matthew Vandermast (ghodges14(AT)msncomcast.comnet), Mar 02 2003

#3 by N. J. A. Sloane at Sat Jun 12 03:00:00 EDT 2004

CROSSREFS

Cf. A080997, A080998; , also A081029, the highly central integers (a subset of this sequence). Complement is A081001.

KEYWORD

nonn,new

nonn

#2 by N. J. A. Sloane at Thu Feb 19 03:00:00 EST 2004

COMMENTS

1, 2, 3, 4, 21 and 27 are currently the only known examples of n that rank exactly nth n-th in centrality; it is not known whether there are others.

KEYWORD

nonn,new

nonn

#1 by N. J. A. Sloane at Fri May 16 03:00:00 EDT 2003

NAME

n is a member if and only if it ranks among top n positive integers in centrality (cf. A080997 for fuller description of this concept).

DATA

1, 2, 3, 4, 6, 8, 10, 12, 14, 15, 16, 18, 20, 21, 24, 27, 28, 30, 32, 36, 40, 42, 44, 45, 48, 50, 52, 54, 56, 60, 63, 64, 66, 68, 70, 72, 75, 76, 78, 80, 84, 88, 90, 96, 98, 99, 100, 102, 104, 105, 108, 110, 112, 114, 117, 120

OFFSET

1,2

COMMENTS

1, 2, 3, 4, 21 and 27 are currently the only known examples of n that rank exactly nth in centrality; it is not known whether there are others.

FORMULA

The formula for the centrality of an integer is A018804(n)/n^2; see also A080997.

CROSSREFS

Cf. A080997, A080998; also A081029, the highly central integers (a subset of this sequence). Complement is A081001.

KEYWORD

nonn

AUTHOR

Matthew Vandermast (ghodges14(AT)msn.com), Mar 02 2003

STATUS

approved