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7 (number)

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

Divisibility RuleEdit

  • 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.



  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   is the root number and   is the last digit. Then   is the whole number. If the whole number ( ) is divisible by 7,   is also a multiple of 7. And   also divide 7. That proves   is divisible seven, since 3 and 6 are both multiples of 3. So   is also divisible by 7.

In the worldEdit

  • 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)


  1. Divisibility rule by 7accessed 21 October 2016