Short story where the protagonist is the number 5 (or 7?)

Question

Another question triggered my memory of a different story, this one short, likely Omni in the 1980s.

A former child prodigy and now professional mathematician works at a sealed think-tank, I think in the deserts in the US southwest. He begins getting visits from a woman and mistakenly mentions this to the head of security, who is an almost twin for the person he thought he was talking to.

The next time she visits the security team breaks in to his room find them gone, leaving behind only a sort of wooden idol, broken in half and sickly green along the break. They tear the place apart to find them, finding only long forgotten microphones.

The woman was actually his sister, the number 6, and he was really 5. Both returned to the Cartesian plane of pure math. That might sound dumb, but it really was a pretty engaging story.

Answer 1

Got it. A Rite of Spring by Fritz Leiber. From the Mathematical Fiction Database:

Leiber has stretched out a very flimsy story line into a 50-page trivia-fest on the number seven. A genius of a mathematician yearns for his childhood ability to visualize and play with mathematics as if it were a real, physical space in which he could move mentally at will - sadly, that ability withered away as he matured. He ends up beseeching the "Great Mathematician" to return him to that mathematical realm or end his life. [Ironically, it is the mathmatician's firm belief that Mathematics is just a game and numbers have no independent existence outside of human mind, despite his longing for the mathematical space...]

Almost immediately after his invocation, an alluring woman, ostensibly from the Pythagorean space where numbers are real, appears at his front door. They end up playing a very, very long word game involving the number seven (which is witty at times and quite tedious at others). Along the way, the mathematician launches several harangues against Pythagorean mysticism, Newton's alchemy, etc. Finally - and after substantial sexual innuendo and explicitendo - the woman and the mathematician vanish when he breaks a strange figurine belonging to the woman; the implication is that they have retired to the Platonic world of forms.

Rite of Spring was published in the collection Universe 7, edited by Terry Carr, Doubleday 1977

Rite of Spring was also nominated for Best Novelette Nebula award in 1977.