OFFSET
0,2
COMMENTS
In other words, a(n) is the number of products of 2*n generators in the braid group B_3 which are equal to the identity element of the group.
Only braids with an even number of crossings are considered because a braid with an odd number of crossings cannot be trivial.
If we do include the 0s corresponding to the odd values of the number of crossings, a group-theoretical name for this sequence is the cogrowth sequence of B_3.
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Alexei Vernitski, Jul 08 2022
STATUS
approved