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A177561
Number of permutations of 2 copies of 1..n avoiding adjacent step pattern up, down, up, down
0
1, 6, 74, 1730, 62340, 3258982, 232475188, 21711360018, 2576183815724, 378267268113542
OFFSET
1,2
CROSSREFS
Sequence in context: A317344 A357011 A231691 * A269334 A069852 A266574
KEYWORD
nonn
AUTHOR
R. H. Hardin May 10 2010
STATUS
approved