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08 Oct 2016, 05:15
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GMAT Club math book Error
all prime numbers above 3 are of the
form (6n-1) or (6n+1) , because all other numbers are divisible by 2 or 3.
my take is that " all other numbers are divisible by 2 or 3" , this aint true e.g. 25, 49. where am i going wrong if you plz Bunuel?
all prime numbers above 3 are of the
form (6n-1) or (6n+1) , because all other numbers are divisible by 2 or 3.
my take is that " all other numbers are divisible by 2 or 3" , this aint true e.g. 25, 49. where am i going wrong if you plz Bunuel?
08 Oct 2016, 06:01
Kudos
Bookmarks
yezz
GMAT Club math book Error
all prime numbers above 3 are of the
form (6n-1) or (6n+1) , because all other numbers are divisible by 2 or 3.
my take is that " all other numbers are divisible by 2 or 3" , this aint true e.g. 25, 49. where am i going wrong if you plz Bunuel?
all prime numbers above 3 are of the
form (6n-1) or (6n+1) , because all other numbers are divisible by 2 or 3.
my take is that " all other numbers are divisible by 2 or 3" , this aint true e.g. 25, 49. where am i going wrong if you plz Bunuel?
Because those are squares of prime numbers. I
Sent from my iPhone using GMAT Club Forum mobile app
08 Oct 2016, 07:25
Kudos
Bookmarks
yezz
GMAT Club math book Error
all prime numbers above 3 are of the
form (6n-1) or (6n+1) , because all other numbers are divisible by 2 or 3.
my take is that " all other numbers are divisible by 2 or 3" , this aint true e.g. 25, 49. where am i going wrong if you plz Bunuel?
all prime numbers above 3 are of the
form (6n-1) or (6n+1) , because all other numbers are divisible by 2 or 3.
my take is that " all other numbers are divisible by 2 or 3" , this aint true e.g. 25, 49. where am i going wrong if you plz Bunuel?
That's not what is said there.
First of all there is no known formula of prime numbers.
Next:
Any prime number \(p>3\) when divided by 6 can only give remainder of 1 or 5 (remainder can not be 2 or 4 as in this case \(p\) would be even and remainder can not be 3 as in this case \(p\) would be divisible by 3).
So any prime number \(p>3\) could be expressed as \(p=6n+1\) or\(p=6n+5\) or \(p=6n-1\), where n is an integer >1.
But:
Not all number which yield a remainder of 1 or 5 upon division by 6 are prime, so vise-versa of above property is not correct. For example 25 yields a remainder of 1 upon division be 6 and it's not a prime number.
Hope it's clear.
