Number of rotation subgroups of S_n
N. J. A. Sloane
njas at research.att.com
Mon Oct 10 20:18:40 CEST 2005
A friend suggested the following set of sequences
Let S_n be the symmetric group of all perms of n letters,
of order n!
A transposition is a permutation like (3,5).
A reflection is any element of order 2, that is, a product
of disjoint transpositions
A "rotation" is a product of two transpositions, not necessarily disjoint,
so either (1,2,3) or (1,2)(3,4), etc.
Questions:
How many subgroups of S_n have the property that they are
generated by rotations?
How many non-isomorphic ones?
How many subgroups of S_n have the property that they are
generated by reflections? (Is this the Bell numbers, A000110 ?)
How many non-isomorphic ones? (Again, this may be a well-known sequence)
Same two questions for groups generated by rotations AND reflections?
NJAS
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