$\{n | n \in \mathbb N \text{ and } n\cdot n + n \text{ is a multiple of } 5 \text { and } n \leq 12\}$
I put $\{4,5,9,10\}$ but apparently this is still a proper set not the complete answer?
$\{n | n \in \mathbb N \text{ and } n\cdot n + n \text{ is a multiple of } 5 \text { and } n \leq 12\}$
I put $\{4,5,9,10\}$ but apparently this is still a proper set not the complete answer?
To make the search easier, I would think of $n*n +n$ as $n * ( n + 1)$, so then you just have to multiply consecutive digits together as see if there is a $5$ as the last digit. This gives the four values you give, along with 0.