Even if a or b is 1 modulo 10
means. And of course zetafunc is correct ending in a 1 does not guarantee primality.
]]>But is that really any better than, say, the Sieve of Eratosthenes?
You would have thought knowing what a and b end in you could determine that a number is composite and therefore not prime, turns out it doesn't seem to work that way.
It wouldn't -- using your notation, x is prime iff (a,b) = (1, x) or (x,1). Even if a or b is 1 modulo 10, that doesn't guarantee that a or b is 1, and for large x, will give you a very large number of possibilities.
I still don't get this post..................? Is 1 modulo 10 a mathematical way of saying, ends in 1.....? I was trying to prove x is composite not prime......? a or b ending in 1 wouldn't guarantee x is prime...?
]]>x! is factorable by x only once when x is prime and more than once when x is not prime. This only happens when x>4.
If x=ab, ab occurs more than once, i.e. x!=axbxabx?
If x=
, occurs more than once i.e. x!=ax2ax. Unless =2 or less and x= 4 or1. a>2 is fine.I think this is simpler than x/x! factors down when x is not prime and doesn't when x is prime!
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Even if a or b is 1 modulo 10, that doesn't guarantee that a or b is 1, and for large x, will give you a very large number of possibilities.
If x = (10c + d)(10e + f) where d and f = 1,3,7 or 9 I just have to prove c and e > 0 granted that x is not factorable by 2,5,3,7. i.e. a and b > 10.
I know how to prove x is not factorable by 2,3,5 or 7, I don't know how to prove that c and e are both >0.
But say I knew what d and f were, you would have thought I'd be able to work out what c and e were................ Don't you think?
]]>You would have thought knowing what a and b end in you could determine that a number is composite and therefore not prime, turns out it doesn't seem to work that way.
It wouldn't -- using your notation, x is prime iff (a,b) = (1, x) or (x,1). Even if a or b is 1 modulo 10, that doesn't guarantee that a or b is 1, and for large x, will give you a very large number of possibilities.
]]>Like this?
More like this;
x is not factorable by 2 or 5.
x = ab
x ends in 1; a and b end in (1,1)(3,7) or (9,9).
x ends in 3; a and b end in (1,3) or (7,9).
x ends in 7; a and b end in (1,7) or (3,9).
x ends in 9; a and b end in (1,9)(3,3) or (7,7).
i.e. 3x9=27.......ends in 7.
by knowing what x ends in we can determine what a and b might end in.
You would have thought knowing what a and b end in you could determine that a number is composite and therefore not prime, turns out it doesn't seem to work that way.
]]>I am working on finding a solution to proving whether a number is prime or not
Like this?
]]>So what are you guys working on?
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