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
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Nov 20 2006
STATUS
approved