Hi Pascal,

You are right this is not ir.sequence,

This number is generated from the JavaScript file located at addons/point_of_sale/static/src/js/models.js

In this file you can find one model names "Order", inside this model one method is there which is responsible for this sequence. Please have a look below for that method.

 // Generates a public identification number for the order.
 // The generated number must be unique and sequential. They are made 12 digit long
 // to fit into EAN-13 barcodes, should it be needed 
 generateUniqueId: function() {
     function zero_pad(num,size){
         var s = ""+num;
         while (s.length < size) {
         s = "0" + s;
         }
         return s;
     }
 return zero_pad(this.pos.pos_session.id,5) +'-'+
 zero_pad(this.pos.pos_session.login_number,3) +'-'+
 zero_pad(this.sequence_number,4);
 },

You can make changes according to your need.

I am sure that it will help a lot.

Thanks.