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A comment on Is this prime?. Parent comment

Re:Is this prime? by noobie on Tuesday March 08, 2016 @11:20AM (#11246182)
For me it's 17, 17*3= 51 which at a first quick glance looks like a prime, up until you add the digits and it's clear of course.
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Re:Is this prime? by jemfinch on Tuesday March 08, 2016 @11:54AM (#11246495)
Use the test for divisibility by 3: if the sum of the digits is divisible by 3, the number is divisible by 3. 5+1=6, so 51 is divisible by 3.
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Re:Is this prime? by noobie on Tuesday March 08, 2016 @02:50PM (#11247985)
Oh yeah, that's what I meant by saying "up until you add the digits and it's clear of course.". It's just an instant observation I guess.
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Re:Is this prime? by borkabrak on Tuesday March 08, 2016 @12:18PM (#11246678)
That's one where experience playing darts really helps. :-)
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Re:Is this prime? by notJim on Tuesday March 08, 2016 @01:26PM (#11247278)
Where I'm from, 17 and 51 are two freeways that run kinda parallel to each other, so that was an easy one for me.
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