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A061207
Number of subgroups of index n of the braid group on 3 strands <a,b|aba=bab>= <c,d|c^2=d^3>, the fundamental group of the complement of a trefoil knot.
0
1, 1, 4, 9, 6, 22, 43, 49, 130, 266, 287, 786, 1730, 2199, 5184, 12193, 17035, 37786, 88959, 136814, 288292, 682573, 1118997, 2307154, 5428806, 9409518
OFFSET
1,3
COMMENTS
Found by counting homomorphisms to the symmetric group.
EXAMPLE
The 4 subgroups of the braid group on 3 strands of index 3 are the 3 stabilizers of one strand and the subgroup of words of total weight divisible by 3.
CROSSREFS
Sequence in context: A075065 A141553 A095065 * A362436 A140694 A152454
KEYWORD
nonn,nice,more
AUTHOR
Douglas Zare, May 30 2001
STATUS
approved