Do graceful graphs exist with more than any arbitrarily large number of vertices, all of which are labelled with a prime or non-negative square number.

Recall that a *graceful* graph is a graph with *m* edges whose vertices can be labelled with some subset of the integers between 0 and *m* inclusive, no two vertices sharing a label, and each of its edges uniquely identified by the absolute difference between its end points (so that this magnitude lies between 1 and *m* inclusive).

There is evidence (https://math.stackexchange.com/questions/3253495/integers-as-differences-of-squares-and-primes/3253666#3253666) that the answer to this is no, but a proof is lacking.