OFFSET
0,3
COMMENTS
A partially ordered set is ranked if there is a function from the poset elements to the integers such that the function value of a covering element is precisely one larger than the function value of the covered element. This is called graded by some authors.
LINKS
Andrew Howroyd, Table of n, a(n) for n = 0..40
EXAMPLE
For n=5, A000112(n) - a(n) = 63 - 61 = 2 because we have 2 posets with 5 elements that are not ranked: a<b<c<d a<e<d and a<c<e a<d b<d b<e where < means "is covered by". - Geoffrey Critzer, Oct 29 2023
PROG
(Sage) sum(1 for P in posets(n) if P.is_ranked())
(PARI) \\ See PARI link in A361953 for program code.
A361920seq(20) \\ Andrew Howroyd, Apr 01 2023
CROSSREFS
KEYWORD
nonn
AUTHOR
Martin Rubey, Mar 29 2023
EXTENSIONS
Terms a(8) and beyond from Andrew Howroyd, Mar 31 2023
STATUS
approved