If elements with a principal quantum number $n>4$ were not allowed in nature, the number of possible elements would be

The maximum number of electrons in an orbit are $2n^{\mathit{2}}$. If $n>4$, is not allowed, then the number of maximum electrons that can be in first four orbit are:

2(1)² + 2(2)² + 2(3)² + 2(4)² = 2 + 8 + 18 + 32 = 60

Therefore, possible elements can be 60.