Number of subgroups of index 4 in free group of rank n+1.
A049295
Number of subgroups of index 4 in free group of rank n+1.
Terms
- a(0) =1a(1) =71a(2) =2143a(3) =54335a(4) =1321471a(5) =31817471a(6) =764217343a(7) =18344733695a(8) =440294408191
External references
- oeis: A049295