Analog Pin 6/7

Dose anyone know how to use analog pin 6/7 as digital outputs tried the following and it has no effect (i am using a Nano)

pinMode(20, OUTPUT); digitalWrite(20, LOW);

What does the processor data sheet say?

i have the output on the Arduino Nano.

http://arduino.cc/en/Main/ArduinoBoardNano

That isn't the processor data sheet. The additional anlogue inputs are simply connected to the analogue input mux, they don't have digital input capability.

can i use them as digital outputs?

No

ok thanks for your help