FrancophonIA/Vikidia-EnFr huggingface dataset:
The number seven is a natural number that comes after six and before eight. In Roman numerals, it is VII.

In mathematics, the number seven is an odd number and a prime number.
It is also a Mersenne prime.

Example

918785

77 is divisible by 7, so the original number 918785 is also divisible by 7.

Proof:
Pretend 



a


{\displaystyle a}

 is the root number and 



b


{\displaystyle b}

 is the last digit. Then 



10
a
+
b


{\displaystyle 10a+b}

 is the whole number.
If the whole number (



10
a
+
b


{\displaystyle 10a+b}

) is divisible by 7, 



3
a
+
b


{\displaystyle 3a+b}

 is also a multiple of 7. And 



(
3
a
+
b
)
−
7
b
=
3
a
−
6
b


{\displaystyle (3a+b)-7b=3a-6b}

 also divide 7. That proves 



3
a
−
6
b


{\displaystyle 3a-6b}

 is divisible seven, since 3 and 6 are both multiples of 3. So 



a
−
2
b


{\displaystyle a-2b}

 is also divisible by 7.