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A123903 Total number of "Emperors" in all tournaments on n labeled nodes. 9
0, 1, 2, 6, 32, 320, 6144, 229376, 16777216, 2415919104, 687194767360, 387028092977152, 432345564227567616, 959230691832896684032, 4231240368651202111471616, 37138201178561408246973726720, 649037107316853453566312041152512, 22596875928343569839364720024765857792 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

An "Emperor" is a player who beats everybody else.

a(n) is the number of isolated nodes in all simple labeled graphs on n nodes. - Geoffrey Critzer, Oct 19 2011

LINKS

Alois P. Heinz, Table of n, a(n) for n = 0..50

S. B. Maurer, The king chicken theorems, Math. Mag., 53 (1980), 67-80.

FORMULA

a(n) = n*2^((n-1)*(n-2)/2).

E.g.f.: x * Sum_{n>=0} 2^C(n,2) x^n/n!. - Geoffrey Critzer, Oct 19 2011

a(n) = n * A006125(n-1). - Anton Zakharov, Dec 21 2016

MAPLE

a:= n-> n*2^((n-1)*(n-2)/2):

seq(a(n), n=0..20);  # Alois P. Heinz, Aug 26 2013

MATHEMATICA

a=Sum[2^Binomial[n, 2]x^n/n!, {n, 0, 20}];

Range[0, 20]!CoefficientList[Series[x a, {x, 0, 20}], x]

Table[n*2^Binomial[n-1, 2], {n, 0, 20}] (* G. C. Greubel, Aug 06 2019 *)

PROG

(Maxima) A123903(n):=n*2^((n-1)*(n-2)/2)$ makelist(A123903(n), n, 0, 17); /* Martin Ettl, Nov 13 2012 */

(PARI) vector(20, n, n--; n*2^binomial(n-1, 2)) \\ G. C. Greubel, Aug 06 2019

(MAGMA) [n*2^Binomial(n-1, 2): n in [0..20]]; // G. C. Greubel, Aug 06 2019

(Sage) [n*2^binomial(n-1, 2) for n in (0..20)] # G. C. Greubel, Aug 06 2019

(GAP) List([0..20], n-> n*2^Binomial(n-1, 2)); # G. C. Greubel, Aug 06 2019

CROSSREFS

Cf. A123553, A125031, A006125.

Sequence in context: A277475 A277484 A005736 * A172401 A272661 A005742

Adjacent sequences:  A123900 A123901 A123902 * A123904 A123905 A123906

KEYWORD

nonn

AUTHOR

N. J. A. Sloane, Nov 20 2006

STATUS

approved

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Last modified February 24 04:36 EST 2020. Contains 332197 sequences. (Running on oeis4.)