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A127697 Number of permutations of {1,2,...,n} where adjacent elements differ in value by 3 or more. 2
1, 1, 0, 0, 0, 0, 2, 32, 368, 3984, 44304, 521606, 6564318, 88422296, 1272704694, 19521035238, 318120059458, 5491779703870, 100150978723568, 1924351621839740, 38864316540425434 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,7

COMMENTS

Equivalently, number of permutations of {1,2,...,n} where elements that differ by 1 in value are neither in positions i and i+1 (adjacent), nor i and i+2.

LINKS

Table of n, a(n) for n=0..20.

EXAMPLE

Valid permutations of {1,...,6} are 415263 and 362514.

CROSSREFS

Cf. A002464 (stride >= 2), A179957 (stride >= 4), A179958 (stride >=5).

Sequence in context: A060868 A270445 A199019 * A191467 A282881 A230567

Adjacent sequences:  A127694 A127695 A127696 * A127698 A127699 A127700

KEYWORD

nonn

AUTHOR

Richard Forster (gbrl01(AT)yahoo.co.uk), Apr 11 2007, Apr 26 2007

EXTENSIONS

Jul 01 2010: Zak Seidov corrected a(10) and a(11). R. H. Hardin then computed a(12) through a(18).

Corrected first term to 1 (was 0).

a(0), a(19)-a(20) from Alois P. Heinz, Oct 27 2014

STATUS

approved

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Last modified November 17 19:40 EST 2017. Contains 294834 sequences.