Sorry to confuse you... @Costas and myself were just having a discussion back and forth about the overall totals and values.
If you are powering your flame sensor on 3.3v then you shouldn't need any resistor between the sensor and the A0 pin.
However if you are powering the sensor with 5v, then you should have a 180K resistor inline with the sensor and the A0 pin. I don't know if this sensor simply detects the flame or can also determine the "amount" or intensity of the flame.
If all you need is a binary HIGH/LOW, then you simply need to make sure that the resistor is large enough to protect the A0 pin from seeing more than it's rated 3.3v maximum limit.
If however you have a 0v-5v signal and you want to precisely scale it's range, then you need to keep the resistor at 180K, since if you go with a higher value resistor, then you can account for the change with calibration, but will lose some resolution.