OFFSET
0,2
COMMENTS
a(n) = number of directed column-convex polyominoes of area n+5 having along the lower contour exactly two reentrant corners. - Emeric Deutsch, May 21 2003
LINKS
Michael De Vlieger, Table of n, a(n) for n = 0..3297
Robert Davis, Greg Simay, Further Combinatorics and Applications of Two-Toned Tilings, arXiv:2001.11089 [math.CO], 2020.
A. F. Y. Zhao, Pattern Popularity in Multiply Restricted Permutations, Journal of Integer Sequences, 17 (2014), #14.10.3.
Index entries for linear recurrences with constant coefficients, signature (8, -25, 38, -28, 8).
FORMULA
G.f.: 1/(((1-2*x)^3)*(1-x)^2).
a(n) = (n^2-n+4)2^(n+1)-7-n - Emeric Deutsch, May 21 2003
a(0)=1, a(1)=8, a(2)=39, a(3)=150, a(4)=501, a(n) = 8*a(n-1)- 25*a(n-2)+ 38*a(n-3)-28*a(n-4)+8*a(n-5). [Harvey P. Dale, Nov 07 2011]
MATHEMATICA
Table[(n^2-n+4)2^(n+1)-7-n, {n, 0, 30}] (* or *) LinearRecurrence[ {8, -25, 38, -28, 8}, {1, 8, 39, 150, 501}, 30] (* Harvey P. Dale, Nov 07 2011 *)
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Wolfdieter Lang, May 26 2000
STATUS
approved