List of quotient singularities with index 2

1 basic regular quotient singularity types and 1 irregular quotient singularity types

Singularity type Index
[4] 2
Basic singularity type Second singularity type Third singularity type Index
[3, 3] [3, 2, 3] [3, 2, 2, 3] 2

Reference: R. Blache, "Two aspects of log terminal surface singularities", Abh. Math. Sem. Univ. Hamburg 64 (1994), 59-87