const byte ledPin = 13;
const byte intPin = 6;
volatile byte state = LOW;

void setup() {
  // put your setup code here, to run once:
  pinMode(ledPin, OUTPUT);
  pinMode(intPin, INPUT_PULLUP);
  attachInterrupt(digitalPinToInterrupt(ledPin), blink, CHANGE);
}

void loop() {
  // put your main code here, to run repeatedly:
  digitalWrite(intPin, state);
}

void blink() {
  state = !state;
}