A363785 A variant of payphone permutations: given a row of n payphones, a(n) is the number ways for n people to choose the payphones in order, where each person chooses an unoccupied payphone such that the closest occupied payphone is as distant as possible, and a payphone adjacent to a single occupied payphone is preferred over a payphone sandwiched between two occupied payphones.

1, 2, 4, 6, 16, 28, 120, 264, 576, 2784, 11040, 37440, 204672, 679680, 2511360, 15655680, 52945920, 232796160, 2456801280, 11867627520, 97875025920, 576737280000, 4012233523200, 20013325516800, 215802239385600, 1778700504268800, 9687506721177600, 88613303353344000, 448250987623219200

Offset

1,2

Links

Max Alekseyev, Table of n, a(n) for n = 1..100

Max A. Alekseyev, Enumeration of Payphone Permutations, arXiv:2304.04324 [math.CO], 2023.

Crossrefs

Cf. A358056, A095236, A095239, A095912, A361294, A361295, A361296, A362192, A363785.

Sequence in context: A098426 A365639 A279480 * A045665 A133492 A045663

Adjacent sequences: A363782 A363783 A363784 * A363786 A363787 A363788

Keyword

nonn

Author

Max Alekseyev, Jun 21 2023

Status

approved