OFFSET
0,2
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.
LINKS
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>=4} k * A274207(k,n).
CROSSREFS
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Jun 14 2016
STATUS
approved