$$\{n | n \in \mathbb N \text{ and } n\cdot n + n \text{ is a multiple of } 5 \text { and } n \leq 12\}$$
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?