Here's something to consider.
Your code only works if the LEDs are attached to sequentially numbered pins, which lacks flexibility. Here I've held the pin numbers in an array and then I can just process the array. With this approach the LEDs do not have to be on sequential pins and another LED could be added easily by adding it's pin number to the ledPin array and changing MAX_PINS to suit.
I did not compile or otherwise test the following:
byte ledPin[] = {5, 6, 7} // array of pin numbers
define MAX_PINS 3 // change to match number of pins used
void setup(){
for (byte i = 0; i < MAX_PINS; i++)
{
pinMode(ledPin[i], OUTPUT); // set up all the pins as output
}
}
void loop(){
for (byte i = 0; i < MAX_PINS; i++) // blink each led separately one after the other
{
digitalWrite(ledPin[i], HIGH);
delay(1000);
digitalWrite(ledPin[i], LOW);
delay(1000);
}
}