Beyond literal counting, this is the start of a famous nursery rhyme:
一二三四五，上山打老虎，老虎不吃人，专吃熊猫精 ('One two three four five, go up the mountain to hunt a tiger; the tiger doesn't eat people, it eats panda spirits') - used to assign roles in children's games or just for syllable practice. As a set expression 'tell me the
一二三四五' means 'tell me every detail in order'.
