First Answer (Riddle):
Here is a riddle I made up:
All Around the Park.
I am repelled by cricket when hit out of the park.
Discard the led, and what is by, to find my mark.
My number is found on a blanket in the park.
Bring some food, and a replacement, to find it at the start.
You have learnt about me, but not first at the park.
Eventually, my line meets from the curve of my arc.
Now look at the tallest and get rid of the eyes.
In a scramble, you will notice my shape in disguise.
The answer is achieved like this:
All Around the Park.
The answer is a circle. It is round and the following clues support it.
I am repelled by cricket when hit out of the park.
Discard the led, and what is by, to find my mark.
I am repelled by cricket when out of the park $\to$ I'm repel cricket when out of the park $\to$ circle written backwards.
A cricket ball (the shape of a circle) can be hit out of the ballpark.
My number is found on a blanket in the park.
Bring some food, and a replacement, to find it at the start.
Bring some food with a blanket in the park, and the replacement word of that scenario is a picnic.
The number pi $\pi$ is found at the start of the word.
You have learnt about me, but not first at the park.
Eventually, my line meets from the curve of my arc.
You are taught about circles at school (which contains two circles, funnily enough), and not at the park.
Circles also have a line (and only one) that meets its other end when drawn (due to its arc).
Now look at the tallest and get rid of the eyes.
In a scramble, you will notice my shape in disguise.
Look at the tallest letters; the capitals. Then, get rid of the $\verb|I|$s (the eyes).
You will have the letters $D,M,B,Y,E,N$ which you can scramble in order to write the words, $MY \ BEND$ which is the shape (or more particularly, "my shape", where shape $=$ bend) that a circle takes place in.
Although the word circle is not mentioned once in the above riddle, it is definitely cleverly hidden and written. Perhaps I could instead name the riddle as, "Going in Circles All Around the Park".
$$\LARGE\between$$
Second Answer (Math):
Here is a puzzle I made:
Suppose you constructed $m$ rows in the following way ($m,n$ are integers): $$\begin{align}&1,2,3,\ldots ,n \\ &n+1,\ldots , 2n \\ &2n+1,\ldots 3n\end{align}$$ $$\vdots$$ $$n(m-1)+1,\ldots, mn$$ In each row, you want to have an odd number of odd primes. If $m<13$, what prime number $n$ can you find that will form the highest possible prime value of $m$?
The answer is also hidden in the puzzle, but reveals itself a bit more...
A solution could be $4843$, but that is not prime (composite); $4843=29\times 167$ and therefore $m\neq 4843$. There are however two solutions, one of them being $m=165941$ (although that is greater than $13$), and the other one being the intended answer.