도전!

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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.


자 모두 한번 풀어 BoA 요~

간신히 엔지니어 소리는 들을 수 있을듯. +_+
And