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A177292
Number of permutations of 3 copies of 1..n with all adjacent differences <= 2 in absolute value.
0
1, 1, 20, 1680, 51240, 1173512, 31006978, 788946320, 18721725280, 435630242080, 9998202729808, 225310437716462
OFFSET
0,3
COMMENTS
a(n) = (3n)!/6^n for n<=3.
CROSSREFS
Cf. A014606.
Sequence in context: A177620 A177632 A177631 * A266737 A177599 A177600
KEYWORD
nonn
AUTHOR
R. H. Hardin, May 06 2010
EXTENSIONS
a(0) and a(11) from Alois P. Heinz, Jan 18 2016
STATUS
approved