

A095912


Variant of the payphone sequence A095236. Here a slot at the end of the row is always preferred over a slot sandwiched immediately between two used slots.


1



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
(list;
graph;
refs;
listen;
history;
text;
internal format)



OFFSET

1,2


LINKS

Table of n, a(n) for n=1..25.


EXAMPLE

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.


CROSSREFS

Cf. A095236, A095239, A095240, A095923.
Sequence in context: A087997 A177905 A118405 * A143474 A261341 A220423
Adjacent sequences: A095909 A095910 A095911 * A095913 A095914 A095915


KEYWORD

nonn


AUTHOR

Jon Wild, Jul 13 2004


EXTENSIONS

Corrected and extended by Don Reble (djr(AT)nk.ca), Jul 15 2004


STATUS

approved



