Interrupts not working on Arduino Mega 2560[Solved]

I just got my arduino mega 2560 and I hooked it up to my encoders for my robot project. They are just photointerrupters so they put out a state change for every 24th of a rotation of the motor. I hooked them up to pins 2 and 3 but when I run this code:

int pin = 13;
volatile int state = LOW;

void setup()
{
  pinMode(pin, OUTPUT);
  attachInterrupt(2, blink, CHANGE);
}

void loop()
{
  digitalWrite(pin, state);
}

void blink()
{
  state = !state;
}

The led doesn't turn on. If I

Serial.println(digitalRead(2));

I see clean high/low pulses. Any ideas? All help is appreciated! Thanks, luketheduke

check which pin has which interupt number 2 is pin 21

Thanks that got it working! luketheduke