TomDavies92
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 Feb 25 awarded Popular Question Oct 27 awarded Famous Question Sep 12 comment If $x$ and $y$ are prime and $y^2+y$ divides $x^2+x$ then $\frac12(x-y)$ is composite oh, ok. To be exact: having $y+1 \mid x-y$ why is it always true, that $y+1 \mid \frac{x-y}{2}$? Sep 12 comment If $x$ and $y$ are prime and $y^2+y$ divides $x^2+x$ then $\frac12(x-y)$ is composite I have one more question: "Since neither $y=2$ nor $y+1=2$, we therefore have that $y \mid \frac{x-y}{2}$ or $y+1 \mid \frac{x-y}{2}$". Let's say x=7 and y=3 - it works with $y+1 \mid x-y$ (4 divides 7-3=4), but it's not working with: $y+1 \mid \frac{x-y}{2}$ (4 does not divide 2) Sep 12 accepted If $x$ and $y$ are prime and $y^2+y$ divides $x^2+x$ then $\frac12(x-y)$ is composite Sep 12 comment If $x$ and $y$ are prime and $y^2+y$ divides $x^2+x$ then $\frac12(x-y)$ is composite Thank you very much for the explanation. I understand everything :). Could you please also add an information why $\frac12(x-y)$ is composite? Sep 12 revised If $x$ and $y$ are prime and $y^2+y$ divides $x^2+x$ then $\frac12(x-y)$ is composite deleted 4 characters in body Sep 12 comment If $x$ and $y$ are prime and $y^2+y$ divides $x^2+x$ then $\frac12(x-y)$ is composite yes, exactly: prime. I'll edit it straightaway, sorry Sep 12 asked If $x$ and $y$ are prime and $y^2+y$ divides $x^2+x$ then $\frac12(x-y)$ is composite Sep 3 comment Find all natural numbers *a*, that satisfy the following: Thank you very much for your hint. I have one more question - I think I solved the problem. Is the correct answer: for n=5 and for n=3? Thank you again for help :) Sep 1 comment Find all natural numbers *a*, that satisfy the following: Thank you for the hint. I'm not exactly sure what do you mean now. Could you clarify your idea? Sep 1 awarded Custodian Sep 1 comment Find all natural numbers *a*, that satisfy the following: sorry for the misleading tag, I've just fixed it. Sep 1 reviewed Approve Find all natural numbers *a*, that satisfy the following: Sep 1 asked Find all natural numbers *a*, that satisfy the following: Jul 25 awarded Famous Question Jun 20 awarded Famous Question May 31 accepted Find all numbers divisible by 25, that begin with 6. May 23 asked Find all numbers divisible by 25, that begin with 6. Mar 28 accepted Prove, that x, y, z fulfill this equation