cp's OEIS Frontend

A382361 Number of nonnesting permutations of the multiset {1,1,2,2,...,n,n} that avoid 123.

%I A382361 #43 Jun 17 2025 01:18:18
%S A382361 1,4,17,82,406,2070,10729,56394,299646,1606816,8683562
%N A382361 Number of nonnesting permutations of the multiset {1,1,2,2,...,n,n} that avoid 123.
%C A382361 Nonnesting permutations of the multiset {1,1,2,2,...,n,n} such that if abcd is a subsequence, then a=d implies b!=c. A permutation avoids 123 if it does not contain any subsequence abc such that a<b<c. For example, 31432142 does not avoid 123 because it contains 134. 34321421 avoids 123.
%H A382361 Robert Dougherty-Bliss, <a href="/A382361/a382361.txt">Python program</a>, May 28 2025.
%H A382361 Sergi Elizalde and Amya Luo, <a href="https://arxiv.org/abs/2412.00336">Pattern avoidance in nonnesting permutations</a>, arXiv:2412.00336 [math.CO], 2024.
%H A382361 Sean A. Irvine, <a href="https://github.com/archmageirvine/joeis/blob/master/src/irvine/oeis/a382/A382361.java">Java program</a> (github)
%o A382361 (Python) # See Robert Dougherty-Bliss link
%Y A382361 Cf. A177555, A383770.
%K A382361 nonn,more
%O A382361 1,2
%A A382361 _Amya Luo_, May 26 2025
%E A382361 a(9)-a(11) from _Sean A. Irvine_, Jun 17 2025