Gotta knock a little harder

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,
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.

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 and resend it to your friends.

Link: hall_of_Fame.xlsx (30.5 KB)

FireJune님 블로그에서 득탬!
나도 일단은 엔지니어니까 5분정도 걸렸나? ㅋㅋ (a, b, c, d, e… -_- 쏘리)