OFFSET
0,2
COMMENTS
a(n) is the absolute value of the chromatic polynomial of the n-hypercube graph evaluated at -1.
LINKS
David Eppstein, 14 acyclic orientations of a square
Eric Weisstein's World of Mathematics, Hypercube Graph
FORMULA
a(n) = Sum_{k=1..2^n} (-1)^(2^n-k) * k! * A334159(n, k). - Andrew Howroyd, Apr 21 2020
a(n) = |Sum_{k=0..2^n} (-1)^k * A334278(n, k)|. - Peter Kagey, Oct 13 2020
EXAMPLE
For n=2, there are 14 ways to orient the edges of a square without cycles (see links).
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Matthew Scroggs, Apr 20 2020
EXTENSIONS
a(5) from Andrew Howroyd, Apr 23 2020
STATUS
approved