|
|
A092880
|
|
Number of ordered 2-multiantichains on an n-set.
|
|
5
|
|
|
1, 2, 6, 26, 126, 602, 2766, 12266, 52926, 223802, 932526, 3844106, 15722526, 63936602, 258902286, 1045109546, 4209004926, 16921851002, 67945160046, 272554432586, 1092540156126, 4377129999002, 17529432313806, 70180474597226
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
0,2
|
|
COMMENTS
|
Let P(A) be the power set of an n-element set A and R be a relation on P(A) such that for all x, y of P(A), xRy if either 0) x is not a subset of y and y is not a subset of x, or 1) x equals y. Then a(n) = |R|. - Ross La Haye, Mar 19 2009
|
|
LINKS
|
|
|
FORMULA
|
a(n) = 4^n - 2*3^n + 2*2^n.
G.f.: (14*x^2-7*x+1) / ((1-2*x)*(1-3*x)*(1-4*x)). - Colin Barker, Dec 10 2012
|
|
MATHEMATICA
|
|
|
PROG
|
(PARI) vector(100, n, n--; 4^n - 2*3^n + 2*2^n) \\ Altug Alkan, Nov 29 2015
(Magma) [4^n - 2*3^n + 2*2^n: n in [0..10]]; // G. C. Greubel, Oct 06 2017
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn,easy
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|