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A129815 Number of reverse alternating fixed-point-free permutations on n letters. 4
0, 0, 1, 2, 6, 22, 102, 506, 2952, 18502, 131112, 991226, 8271792, 73176262, 703077552, 7121578106, 77437418112, 883521487942, 10726837356672, 136104948161786, 1825110309733632 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,4

COMMENTS

From Emeric Deutsch, Aug 06 2009: (Start)

Reverse alternating permutations are called also up-down permutations.

a(n) is also the number of reverse alternating permutations having exactly 1 fixed point (see the Stanley reference). Example: a(4)=2 because we have 1423 and 2314.

(End)

LINKS

Table of n, a(n) for n=1..21.

R. P. Stanley, Alternating permutations and symmetric functions

FORMULA

a(2n-1) = A129817(2n-1). [Emeric Deutsch, Aug 06 2009]

EXAMPLE

a(4)=2 because we have 3412 and 2413. [Emeric Deutsch, Aug 06 2009]

CROSSREFS

Cf. A000111, A000166, A007779.

Sequence in context: A002772 A000140 A079263 * A251181 A103941 A064643

Adjacent sequences:  A129812 A129813 A129814 * A129816 A129817 A129818

KEYWORD

more,nonn

AUTHOR

Vladeta Jovovic, May 20 2007

EXTENSIONS

a(21) from Alois P. Heinz, Jun 11 2015

STATUS

approved

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Last modified October 22 15:11 EDT 2018. Contains 316490 sequences. (Running on oeis4.)