void setup() {
  // put your setup code here, to run once:
  pinMode( 13, OUTPUT );
  pinMode( 7, OUTPUT );
  pinMode( 4, OUTPUT );
}

uint32_t led1_next = 0, led2_next = 0, led3_next = 0;

uint32_t led1_pulse = 1000 / ( 2 * 1 ); // 1Hz
uint32_t led2_pulse = 1000 / ( 2 * 2 ); // 2Hz 
uint32_t led3_pulse = 1000 / ( 2 * 0.67 ); // 0.67Hz 

void loop() {
  // put your main code here, to run repeatedly:
  if( millis() > led1_next )
  {
    led1_next = millis() + led1_pulse;
    digitalWrite( 13, ! digitalRead( 13 ) );
  }

  if( millis() > led2_next )
  {
    led2_next = millis() + led2_pulse;
    digitalWrite( 7, ! digitalRead( 7 ) );
  }

  if( millis() > led3_next )
  {
    led3_next = millis() + led3_pulse;
    digitalWrite( 4, ! digitalRead( 4 ) );
  }

  // other tasks
}