random
long random(long max);
long random(long min, long max);
This function returns a random number from 0 to max - 1, or between min and max. You should call randomSeed() in setup() before using the random number generator.
Usage:
long randomNumber1 = random(1000); //randomNumber1 is somewhere between 0 and 1000.
long randomNumber2 = random(100, 500); //randomNumber2 is somewhere berween 100 and 500.