How is seven different from the rest of the numbers between one and ten? - Answer this no cheating !! (i increased the points now !)
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How is seven different from the rest of the numbers between one and ten?
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17 Answers

Hariharaier Narayanan, former CEO
Answered July 6, 2019
Very interesting question.
If you divide any number other than multiples of 7, by 7, then you will get an unending numbers after the decimal point; the numbers appearing after the decimal point will repeat itself after every six digits.
For example 243/7= 34.714285714285714285——
You see in the above, 714285 repeats continuously. This will not happen only when the number is perfectly divisible by 7.
All integers are divisible by 1; all even numbers are divisible by 2; all numbers whose digits after adding up, if it is divisible by 3, then the number is divisible by 3; in any number if the last two digits are divisible 4, then the number is divisible by 4, if the last digit of a number is 5 or 0, then it is divisible by 5, if the digits of the number after adding up, if divisible by 9, then the number is divisible by 9.
For finding a number divisible by 6, first it should be divisible without reminder by 2. After dividing by 2, add up the digits, if it is divisible by 3, then the number is divisible by 6. Similarly, after dividing the number by 2, if you find the last two digits are divisible 4, then the number is divisible by 8. Any number ending 0, then it is divisible by 10.
Such kind of criteria does not exist to find the divisibility of a number by 7.
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· Answer requested by Becca Veverka
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Saverio Trioni, I studied Surreal Numbers
Answered July 6, 2019
The only reasonable difference is about checking divisibility.
1: ok, everything.
2: last digit is divisible by 2
3: sum of digits is divisible by 3
4: last two digits form a multiple of 4
5: last digit is 0 or 5
6: rules for 2 and 3 at the same time
8: last 3 digits form a multiple of 8
9: sum of digits is divisible by 9
10: last digit is 0
Now 7? Go and divide yourself. 7 is the smallest natural number for which we don’t have a better algorithm/trick than Euclidean division. One could argue that the divisibility by 9 is actually Euclidean division in disguise, but it is much faster mentally. For 7, we have no other choice to perform the actual division step by step until we get to a remainder.
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Kevin Simonson, M.S. Digital Logic Design & Theoretical Computer Science, Paul G. Allen School of Computer Science & Engineer…
Answered July 23, 2019
There’s no easy way to tell whether a number is a multiple of seven. For two, four, and eight, you just look at the last digit of a number, last two digits, or last three digits respectively. For five, you just look at the last digit. For three and nine, you just add up all the digits in the number and see if the sum is divisible by three or nine respectively. For six you use a combination of the two. For seven, on the other hand, you have to do a lot more work.
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· Answer requested by Becca Veverka