7 is the fourth prime number in mathematics. 7 is the fourth mersenne prime, 2 3-1= 7.

It is also a Hudor prime number, the second lucky prime number.

7 is the cubic difference of two numbers: 7 = 2 3-13, and 7 is the smallest positive integer satisfying this property.

999,999 divided by 7 is exactly142,857, so there are six cycles of 1/7, which are repeated all the time.

1/7 = 0. 142857 142...2/7 = 0.2857 14285...3/7 = 0.42857 1428 ...

When the number of sides is less than or equal to six, a regular polygon can be drawn with a ruler, but a regular heptagon cannot.

There is a famous 1/7 law in fluid mechanics. There are actually two differential structures on Milner's strange ball S 7.

All catastrophe phenomena in catastrophe theory are attributed to seven singularity properties.

At 25℃, the PH value of neutral solution is 7.

For example, there are seven Greek sages, seven archbishops, seven virtues, seven capital crimes, seven heavens, seven gifts from God, seven sacraments, seven patron saints, seven goodness and so on. All these fully reflect the extensive application of "Seven" in religious culture.