Hi, Why do some textbooks say that Avogadro's number is 602 sextillion ? I wrote out the full number and wrote the number above each set of zero's and it is 602 hexillion.

Hi Ash

You've miscounted a little there: the second bottom row should be millions ##(10^6)##, not hundreds of thousands. That throws you off by one line all the way through... which means that you do get to sextillion, counting correctly.