# Powers of 102?

Let $$A={102^1, 102^2, 102^3, \cdots}$$. How many primes $$p$$ are there such that $$A$$ has at least one element $$a$$ such that $$a \equiv -1 \text{ (mod p)}$$?

For example, one such prime is $$103$$, because $$102^1 \equiv -1 \text{ (mod 103)}$$.

×