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A007999
a(n)=number of permutations w of 1,2,...,n such that w and w^{-1} are alternating.
+0
2
1, 1, 2, 3, 8, 19, 64, 213, 880, 3717, 18288, 92935, 531440, 3147495, 20525168, 138638825, 1015694832, 7700244745, 62623847536, 526317901451, 4705365925872, 43407723925499, 423149546210416, 4250149857500861, 44868038386273776
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Maintained by
N. J. A. Sloane
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njas@research.att.com
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Last modified December 5 23:38 EST 2009. Contains 170428 sequences.
AT&T Labs Research
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