Problem with A6 & A7

i beginner arduino platform. frost post . i'm using arduino nano board. while using analog inputs pin digital input a0-a5 works great a6,a7 not repond inputs, can pls tell wrong or board damaged

code is

void setup()
{
pinmode(13, output);
pinmode(a7, input_pullup);
}

void loop()
{
   
if(digitalread(a6)==low)
digitalwrite(13,low);
else
digitalwrite(13,high);
}

a6 , a7 not universal other pins. analog

http://forum.arduino.cc/index.php?topic=152724.0

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