In this short story, a number theorist is obsessed with one number, the date of his own death:
(quoted from Final Integer)
It has been said that number theory was once the purest of pure math. But in David’s academic circle, number theory was thought of as rather grotty. After all, it had exchanged its purity for relevance, even sinking so low as to underpin modern electronic commerce. The geometry gang now looked down on David, when they weren’t wasting time on their squabble about whether lowdimensional or highdimensional geometry was superior. Number theory seemed far too specific to them, too finite in scope. After all, even third graders were learning about prime numbers, themselves the poster children for number theory. And by sixth grade, even the little savages were bored with the concept.
If David’s colleagues had known that he had a fixation on one random and essentially uninteresting integer, they would have written him off as a star on the edge of decline. They might not exactly be measuring his office for new drapes, but his status would have fallen.

Then, a professional success and personal tragedy for David "change the equation"...
The author is a former statistics professor and NSA intelligence officer.
Interestingly, this is the second short story about math and death by Willemain that has appeared in the Mathematical Intelligencer in 2021. (See Mathematics Disputes with Death, and the Devil Intervenes .)
Publication information: Willemain, T.R. Final Integer. Math Intelligencer 43, 74–75 (2021). https://doi.org/10.1007/s00283021100786 