Very sad to hear about this. Graham apparently was the informal “administrator” who awarded the remaining prizes for problems set forth by Paul Erdős.

From Wikipedia [0]:

> Throughout his career, Erdős would offer payments for solutions to unresolved problems. These ranged from $25 for problems that he felt were just out of the reach of the current mathematical thinking (both his and others), to several thousand dollars for problems that were both difficult to attack and mathematically significant. There are thought to be at least a thousand remaining unsolved problems, though there is no official or comprehensive list. The offers remain active despite Erdős's death; Ronald Graham is the (informal) administrator of solutions. A solver can get either an original check signed by Erdős before his death (for memento only, cannot be cashed) or a cashable check from Graham.

I wonder if anyone else will continue the tradition.

0: https://en.wikipedia.org/wiki/Paul_Erd%C5%91s