No 9

Let's multiply the first four positive integers together: 1x2x3x4 = 24.
Obviously 5 does not divide 24 but it does divide 1 more than 24.
Now let's try the first five positive integers multiplied together: 1x2x3x4x5 = 120.
This time 6 does divide 120 and does not divide 1 more than 120.
The next case is: 1x2x3x4x5x6 = 720. Does 7 divide this? Does 7 divide 1 more than 720?

n

1x2x...x(n-1)
divides by
n?

1x2x...x(n-1) + 1
divides by
n?

2

1

no

1+ 1

yes

3

1x2

no

1x2 + 1

yes

4

1x2x3

no

1x2x3 + 1

no

5

1x2x3x4

no

1x2x3x4 + 1

yes

6

1x2x3x4x5

yes

1x2x3x4x5 + 1

no

7

1x2x3x4x5x6

no

1x2x3x4x5x6 + 1

yes
Continue this table and observe something amazing about the pattern of yes/no answers in the last column.
What has this to do with a man called Wilson?
 

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