OFFSET
2,2
COMMENTS
FORMULA
For n >= 4: a(n) = 4*A000682(n-2).
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
Roger Ford, Sep 01 2020
STATUS
approved