# 7 (number)

 ← 6 7 8 →
Cardinal seven
Ordinal 7th
(seventh)
Numeral system septenary
Factorization prime
Prime 4th
Divisors 1, 7
Roman numeral VII
Roman numeral (unicode) Ⅶ, ⅶ
Greek prefix hepta-/hept-
Latin prefix septua-
Binary 1112
Ternary 213
Quaternary 134
Quinary 125
Senary 116
Octal 78
Duodecimal 712
Vigesimal 720
Base 36 736
Greek numeral Z, ζ
Amharic
Arabic ٧,7
Persian ٧ - هفت
Urdu
Bengali
Chinese numeral 七(qi)
Devanāgarī (saat)
Telugu
Tamil
Hebrew ז (Zayin)
Khmer
Thai
Pronunciation of the number 7

The number seven is a natural number that comes after six and before eight. In Roman numerals, it is VII.

## Mathematics

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

### Divisibility Rule

• To test if an integer is divisible by 7 or not,
1. Take off the last digit and multiply it by 2.
2. Subtract the root number from the product .[1]
3. Repeat the second step again and and again until it is clearly that the number is divisible by 7 or not.

Example

918785

1. 5×2=10, 91878-10=91868
2. 8×2=16, 9186-16=9170
3. 0×2=2, 917-0=917
4. 7×2=14, 91-14=77

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

Proof: Pretend ${\displaystyle a}$ is the root number and ${\displaystyle b}$ is the last digit. So ${\displaystyle 10a+b}$ is the whole number. If the whole number (${\displaystyle 10a+b}$)is divisible by 7, that means ${\displaystyle 3(10-7)a+b}$ is also a multiple of 7. And ${\displaystyle (3a+b)-7b=3a-6b}$ must also divide 7. ${\displaystyle 3a-6b}$ is always divisible by 3, since 3 and 6 are all multiples of 3, through 3 is coprime to 7, and the last, ${\displaystyle a-2b}$ is also divisible by 7.

## In the world

• There are seven colors in the rainbow.
• The atomic number of nitrogen.
• The number of horizontal rows of elements in the periodic table.
• Seven gates of heaven (QUR'AN 15th chapter AL-HIJR verse 44)915:44)
• Seven days in a week
• Seven seas and seven continents.
• Seven major parts of the human body (2 legs, 2 hands, trunk, neck and head)