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.
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.
Terms
- a(0) =1a(1) =1a(2) =4a(3) =9a(4) =6a(5) =22a(6) =43a(7) =49a(8) =130a(9) =266a(10) =287a(11) =786a(12) =1730a(13) =2199a(14) =5184a(15) =12193a(16) =17035a(17) =37786a(18) =88959a(19) =136814a(20) =288292a(21) =682573a(22) =1118997a(23) =2307154a(24) =5428806a(25) =9409518
External references
- oeis: A061207