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A177284
Number of permutations of 2 copies of 1..n with all adjacent differences <= 3 in absolute value.
1
1, 1, 6, 90, 2520, 41580, 516180, 6068622, 76331906, 958679970, 11679900408, 138047313960, 1610654864328, 18649754961744, 214256589488616, 2439692058769566, 27562317214408488, 309367132582535226, 3453299423388485028, 38354816922190327314, 424048220090513056908
OFFSET
0,3
COMMENTS
a(n) = (2n)!/2^n for n<=4.
LINKS
CROSSREFS
Sequence in context: A177592 A177593 A132467 * A266735 A177564 A177565
KEYWORD
nonn
AUTHOR
R. H. Hardin, May 06 2010
EXTENSIONS
a(0), a(13) from Alois P. Heinz, Jan 14 2016
Terms a(14) and beyond from Andrew Howroyd, May 14 2020
STATUS
approved