

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
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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



