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 A182216 Number of permutations sortable by a double-ended queue. 4
 1, 1, 2, 6, 24, 116, 634, 3762, 23638, 154816, 1046010, 7239440, 51069582, 365879686, 2654987356, 19473381290, 144138193538, 1075285161294, 8076634643892, 61028985689976, 463596673890280, 3538275218777642 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 LINKS Daniel Denton and Peter Doyle, Table of n, a(n) for n = 0..100 Michael Albert, Mike Atkinson, Steve Linton, Permutations generated by stacks and deques, Annals of Combinatorics, 14 (2010) 3-16. (gives method of computation). Daniel Denton, Methods of computing deque sortable permutations given complete and incomplete information, arXiv:1208.1532. Andrew Elvey-Price and Anthony J. Guttmann, Permutations sortable by deques and by two stacks in parallel, arxiv:1508.02273, 2015 Philippe Flajolet, Bruno Salvy and Paul Zimmermann, Lambda-Upsilon-Omega, The 1989 CookBook, page 105. Paul Zimmermann, C program for A182216 P. Zimmermann, Introduction to Automatic Analysis, 2012. EXAMPLE Up to n=4 all permutations can be sorted by a double-ended queue (deque for short). For n=5 the permutation 24351 cannot: you first queue 2 on either side, then 4 on either side, then 3 has to be queued on the same side as 4 otherwise it will "block" 2 between 3 and 4, but then whatever side you queue 5, you will block either 2 (between 4 and 5) or 3 (between 4 and 5). CROSSREFS Cf. A215257, A216040, A215252. Sequence in context: A228395 A082631 A212198 * A097483 A210591 A266332 Adjacent sequences:  A182213 A182214 A182215 * A182217 A182218 A182219 KEYWORD nonn AUTHOR Paul Zimmermann, Apr 19 2012 EXTENSIONS a(13)-a(14) confirmed by Michael Albert, Apr 19 2012 a(16)-a(21) from Michael Albert, Jun 27 2012 a(0)=1 added by N. J. A. Sloane, Sep 12 2012 STATUS approved

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Last modified February 22 23:44 EST 2020. Contains 332157 sequences. (Running on oeis4.)