OFFSET
0,7
COMMENTS
A bargraph is a polyomino whose bottom is a segment of the nonnegative x-axis and whose upper part is a lattice path starting at (0,0) and ending with its first return to the x-axis using steps U=(0,1), D=(0,-1) and H=(1,0), where UD and DU are not allowed.
The site-perimeter of a polyomino is the number of exterior cells having a common edge with at least one polyomino cell.
a(n)^(1/n) tends to 2.222118... . - Vaclav Kotesovec, Jun 26 2016
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..820
M. Bousquet-Mélou and A. Rechnitzer, The site-perimeter of bargraphs, Adv. in Appl. Math. 31 (2003), 86-112.
Wikipedia, Polyomino
FORMULA
a(n) = Sum_{k=floor((n-1)/2)..floor(((n-1)^2+3)/12)} k * A274207(n,k).
CROSSREFS
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Jun 13 2016
STATUS
approved