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7 (number)



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6 7 8
−1 0 1 2 3 4 5 6 7 8 9
Cardinalseven
Ordinal7th
(seventh)
Factorizationprime
Prime4th
Divisors1, 7
Roman numeralVII
Roman numeral (unicode)Ⅶ, ⅶ
Greek prefixhepta-/hept-
Latin prefixseptua-
Binary1112
Ternary213
Quaternary134
Quinary125
Senary116
Octal78
Duodecimal712
Hexadecimal716
Vigesimal720
Base 36736
Greek numeralZ, ζ
Amharic
Arabic٧,7
Persian٧ - هفت
Urdu
Bengali
Chinese numeral七(qi)
Devanāgarī (saat)
Telugu
Tamil
Hebrewז (Zayin)
Khmer
Thai

File:En-us-Seven.ogg


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 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=0, 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 [math]a[/math] is the root number and [math]b[/math] is the last digit. Then [math]10a+b[/math] is the whole number. If the whole number ([math]10a+b[/math]) is divisible by 7, [math]3a+b[/math] is also a multiple of 7. And [math](3a+b)-7b= 3a-6b[/math] also divide 7. That proves [math]3a-6b[/math] is divisible seven, since 3 and 6 are both multiples of 3. So [math]a-2b[/math] 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)

References

  1. Divisibility rule by 7accessed 21 October 2016