Count on Me by Ray Vukcevich (F&SF, October-November 1995) gets off to a very clever start with this:
It didn’t confuse me that the new occupant of apartment 29A was a woman. The Father of Lies is nothing if not inventive. The number 29A is, of course, the Number of the Beast in base 16, and 16 is the atomic number of Sulfur. Base 16 is commonly called “hex.” It was all too obvious.
Celia Strafford looked to be in her early thirties— 32, to be precise, since 2,3, and 37 are the prime factors of 666, and she looked too old to be 23, and I’m 37, and she looked younger than me, so ergo, as they say, 32. I’m speaking of the age of her body; I couldn’t know the age of the creature inside. She wore her long red hair loose down her back. I watched her closely as she stooped to pick up a box to lug up the stairs to her new apartment. She wore cut-off jeans and an abbreviated yellow halter top. Her legs were that strange golden tan you only see on women. I’ve never been able to figure how they achieve that color. She wore no shoes. p. 100
The rest of the beginning of the story sees some conversational sparring between the narrator, Palmer (actually Brother Palmer of the Secret Order of Morse), and Celia, the new neighbour, as well as more numerology (at one point she says, when told that he used to be in the Army, that “there are probably 820 things worse”, which Palmer identifies as 666 in Base 9). Eventually Palmer becomes more and more convinced that she belongs to the Army of the Night, something that is repeatedly confirmed by numerology when they meet later on in her apartment. Then, at a climactic moment (spoiler), he leaps away from her and tries to make the sign of the cross. After a couple more fumbled attempts, Celia giggles and makes the sign herself—and reveals that she is Sister Celia of the Divine Order of Symmetry!
At this point the story almost completely deflates, and the second half of the story is a wodge of number and Morse code crunching that leads them to the message, “ONE GOD”, and the realisation that all is well with the world.
A game of two halves (two in any Base from 3 to Infinity).
** (Average). 3,350 words.