Easy Mathematical Challenge

Gals & Boys,


"This is a mathematical challenge, and it's been said that:
If you're an engineer, you should be able to solve it in (under) three minutes (more like 30 seconds), if you're an architect, in three hours; if you're a doctor, in six hours; if you're an accountant, in three months and if you're a lawyer, probably never.
if you're good at math or logical problems, solve this challenge and the answer is the password to open the spreadsheet to which you can add your name to the hall of fame.
What is the missing number in this logical series?
1, 2, 6, 42, 1806, ____??? "

"The answer is the password to open the spreadsheet that is attached to this email. If you figure it out, open the spreadsheet, type your name in, save it.