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A177291
Number of permutations of 3 copies of 1..n with all adjacent differences <= 1 in absolute value.
2
1, 1, 20, 92, 506, 2288, 10010, 41618, 168284, 664958, 2584442, 9916688, 37679618, 142079906, 532572428, 1987037318, 7386724082, 27381500624, 101272019258, 373902595130, 1378571667644, 5077289249390, 18683930010890, 68709775705328, 252549056389394, 927895845621746
OFFSET
0,3
COMMENTS
a(n) = (3n)!/6^n = A014606(n) for n<=2.
LINKS
CROSSREFS
Column k=3 of A331562.
Cf. A014606.
Sequence in context: A211140 A200431 A172200 * A169711 A281391 A071092
KEYWORD
nonn
AUTHOR
R. H. Hardin, May 06 2010
EXTENSIONS
a(0)=1 prepended by Alois P. Heinz, Jan 21 2020
a(19)-a(20) from Alois P. Heinz, Jan 22 2020
Terms a(21) and beyond from Andrew Howroyd, May 14 2020
STATUS
approved