Consider fully developed laminar flow in a circular pipe of a fixed length:

1) The friction factor is inversely proportional to Reynolds number

2) The pressure drop in the pipe is proportional to the average velocity of the flow in the pipe

3) The friction factor is higher for a rough pipe as compared to a smooth pipe

4) The pressure drop in the pipe is proportional to the square of average of flow in the pipe.

Which of the above statements are correct?