

A337581


a(n) is the number of semimeanders with n top arches that have both an arch of length 1 adjacent to the center of the top arch configuration and an arch of length 1 starting or ending the top arch configuration.


0



1, 2, 4, 8, 16, 40, 96, 264, 696, 2016, 5624, 16840, 48792, 149512, 445112, 1387384, 4215496, 13312752, 41097864, 131146520, 410045672, 1319612232, 4169110888, 13511677040, 43060097728, 140383359392
(list;
graph;
refs;
listen;
history;
text;
internal format)



OFFSET

2,2


COMMENTS

The number of semimeanders with n top arches is A000682(n). The number of semimeanders with n top arches that have a starting or ending arch of length 1 is 2*A000682(n1). The number of semimeanders with n top arches that have an arch adjacent to the center with length 1 is 2*A000682(n1).


LINKS



FORMULA



EXAMPLE

For n = 5: (10) is a starting or ending arch of length 1, [10] is an arch adjacent to the center with length 1, a(5) = 8.
(10)101[10]100, 110[10]010(10), (10)1[10]11000, 11100[10]0(10), (10)111[10]000,
111[10]000(10), (10)1[10]01100, 11001[10]0(10).
/\ = arch with length 1, (10) = arches with length 1 at ends or adjacent to center
/\ /\ /\
/ \ / \ / \
/ /\ \ / /\ \ /\ / \
1 10 0 1(10) 0(10) /\ /\ / /\ /\\
center end (10) 10 1(10)100
end center


CROSSREFS



KEYWORD

nonn,more


AUTHOR



STATUS

approved



