Number of subgroups of index n in free group of rank 3.

A027837

Number of subgroups of index n in free group of rank 3.

Terms

    a(0) =1a(1) =7a(2) =97a(3) =2143a(4) =68641a(5) =3011263a(6) =173773153a(7) =12785668351

External references