A095912 Variant of the pay-phone sequence A095236. Here a slot at the end of the row is always preferred over a slot sandwiched immediately between two used slots.
1, 2, 4, 6, 12, 28, 104, 152, 528, 2208, 9120, 23616, 130944, 278784, 1635840, 14181120, 32186880, 116674560, 1262039040, 2443714560, 58920099840, 161981890560, 1416311930880, 7700720025600, 120779469619200
Offset: 1
Keywords
Examples
Example: there are 5 payphones. First arrival may choose any; he selects phone #2. Next arrival must take the furthest away, #5. Next arrival must take either of #3 or #4 (since both have a neighbor on one side and a vacant slot on the other); he chooses #3. Next arrival must take #1 (because end slots are preferred over "sandwiched" slots), leaving #4 for the last arrival. The permutation (25314) is one of a(5)=10 that satisfy the requirements.
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.
- Simon Wundling, About a combinatorial problem with n seats and n people, arXiv:2303.18175 [math.CO], 2023. (German)
Extensions
Corrected and extended by Don Reble, Jul 15 2004