See MB O”CH 345 s”k 23 who asks the question and says that we only count what the Torah specifically enumerates. There is an interesting implication according to the Maharal who says that 600K is a complete number containinhg 6 like six directions in the shaking the lulav, 100 and 1000. The Rabbenu Bacheya explains that if you take the first letter of each tribe usung Yosef and multiply them by 1000 when you accumulate it, you will get 597,000, 600,00 less 3000 that were killed at the Aigel.
Menu