Talk:7 (number)

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Mark this section for deletion[change source]

I would like to recommend that this section be deleted because there are a number of errors in the math and the text. The test is an interesting math trick but there are many other things that can be added to this article regarding the number seven.I am happy to spend the time to fix the mistakes if consensus finds that the previous information should go back in the article. :
===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 is the root number and is the last digit. So is the whole number. If the whole number ()is divisible by 7, that means is also a multiple of 7. And must also divide 7. is always divisible by 3, since 3 and 6 are all multiples of 3, through 3 is coprime to 7, and the last, is also divisible by 7. Thank you bobdog54 (talk) 13:54, 21 October 2016 (UTC)[reply]

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