

A277556


Number of permutations of n elements in which alternating maximal rises and descents are all of length >= 2.


0



1, 0, 2, 2, 14, 42, 244, 1208, 7930, 52710, 405850, 3310702, 29742388, 285103536, 2943395390
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OFFSET

1,3


COMMENTS

A lengtht rise in a permutation a() is a list of t+1 consecutive values a(i), ..., a(i+t) for which a(i) < a(i+1) < ... < a(i+t), and similarly for a descent. By "maximal" we mean it can't be increased in length on either side. For example, 3 4 5 2 1 6 7 8 has a rise of length 2 (3,4,5), followed by a descent of length 2 (5,2,1), followed by a rise of length 3 (1,6,7,8).


LINKS

Table of n, a(n) for n=1..15.


CROSSREFS

Sequence in context: A226157 A264508 A194689 * A166114 A202730 A292080
Adjacent sequences: A277553 A277554 A277555 * A277557 A277558 A277559


KEYWORD

nonn,more


AUTHOR

Jeffrey Shallit, Nov 16 2016


STATUS

approved



