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A198434
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Number of simple symmetric permutations of degree 2n (or 2n+1).
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0
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2, 10, 90, 966, 12338, 181470, 3018082, 55995486, 1146939010, 25716746430, 626755197698, 16502357651966, 466944932413442, 14133259249586174, 455715081098876418, 15596665064842012158, 564724372634695925762, 21568978799171323200510, 866674159679235417061378, 36548294282449538711357438
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OFFSET
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2,1
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COMMENTS
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A permutation is simple if the only intervals that are fixed are the singletons and [1..m].
A permutation p is symmetric if i+j=m+1 implies p(i)+p(j)=m+1.
For example the permutations
1234 and 12345
2413 25314
are both simple and symmetric.
Symmetric simple permutations of degree 2n+1 correspond to simple permutations in the Weyl group of type B_n.
Symmetric simple permutations of degree 2n correspond to simple permutations in the Weyl group of type C_n.
These occur in pairs so all entries in this sequence will be even.
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LINKS
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R. Dewji, I. Dimitrov, A. McCabe, M. Roth, D. Wehlau and J. Wilson,
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EXAMPLE
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The simple symmetric permutations of lowest degree are 2413, 3142, 25314, 41325.
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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