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A177563
Number of permutations of 2 copies of 1..n avoiding adjacent step pattern up, up, down, down.
0
1, 6, 88, 2328, 96886, 5841912, 482051408, 52197308928, 7182160372912, 1224288015648528, 253281233443497344, 62522722555285781376, 18154991497984902599824, 6126411246446756437747008
OFFSET
1,2
CROSSREFS
Sequence in context: A265267 A218260 A177567 * A177569 A327645 A309165
KEYWORD
nonn
AUTHOR
R. H. Hardin, May 10 2010
EXTENSIONS
a(11)-a(14) from Alois P. Heinz, Nov 02 2013
STATUS
approved