

A202691


Triangle read by rows: number of type B snakes according to their last value.


4



1, 0, 0, 1, 1, 1, 3, 3, 2, 2, 1, 0, 0, 3, 6, 8, 8, 10, 11, 11, 57, 57, 54, 48, 40, 40, 32, 22, 11, 0, 0, 57, 114, 168, 216, 256, 256, 296, 328, 350, 361, 361
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OFFSET

1,7


COMMENTS

"The table counting snakes of type B by their last value is obtained by the following algorithm: first separate the picture by the column p = 0 and then compute two triangles. Put 1 at the top of the left triangle and 0 at the top of the right one and compute the rest as follows: fill the second row of the left (resp. right) triangle as the sum of the elements of the first row (resp. strictly) to their left. Then fill the third row of the right (resp. left) triangle as the sum of the elements of the previous row (resp. strictly) to their right. Compute all rows successively by reading from left to right and right to left alternately." [JoshuatVerges et al.]


LINKS

Table of n, a(n) for n=1..42.
M. JosuatVerges, J.C. Novelli and J.Y. Thibon, The algebraic combinatorics of snakes, arXiv preprint arXiv:1110.5272, 2011


EXAMPLE

Triangle begins:
1 0
0 1 1 1
3 3 2 2 1 0
0 3 6 8 8 10 11 11
57 57 54 48 40 40 32 22 11 0
0 57 114 168 216 256 256 296 328 350 361 361


CROSSREFS

Cf. A185356, A202690, A202704.
Sequence in context: A102905 A020862 A131589 * A278402 A276415 A064983
Adjacent sequences: A202688 A202689 A202690 * A202692 A202693 A202694


KEYWORD

nonn,tabf,more


AUTHOR

N. J. A. Sloane, Dec 22 2011


STATUS

approved



