Why is the serial primary key incrementing despite a using "On Conflict Do Nothing?

I have the below table in PostgreSQL 13: ### table name: newtable field type ----- ---- Seq bigserial code varchar Seq is the primary key (auto-increment) Code is a unique key index Insert Into newtable (Code) Values ('001') On Conflict(Code) Do Nothing --> Seq value is 1 Insert Into newtable (Code) Values ('001') On Conflict(Code) Do Nothing Insert Into newtable (Code) Values ('001') On Conflict(Code) Do Nothing Insert Into newtable (Code) Values ('002') On Conflict(Code) Do Nothing --> Seq value is 4 Why is Seq 4? Is there any way to increase value on successful inserts only?