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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
Mar
28
comment Prove, that x, y, z fulfill this equation
I've just edited the question, I'm sorry for the mistake. Now it seems to be clear :).