Classic fungal number horror from Stephen King’s ‘Gray Matter’:

What we saw in that one or two seconds will last me a liftetime — or whatever’s left of it. It was a huge gray wave of jelly, jelly that looked like a man, and leaving a trail of slime behind it.
But that wasn’t the worst. Its eyes were flat and yellow and wild, with no human soul in ’em. Only there weren’t two. There were four, an’ right down the center of the thing, betwixt the two pairs of eyes, was a white, fibrous line with a kind of pulsing pink flesh showing through like a slit in a hog’s belly.
It was dividing you see. Dividing in two.
Bertie and I didn’t say nothing to each other going back to the store. I don’t know what was going through his mind, but I know well enough what was in mine: the multiplication table. Two times two is four, four times two is eight, eight times two is sixteen, sixteen times two is —
We got back. Carl and Bill Pelham jumped up and started asking questions right off. We wouldn’t answer, neither of us. We just turned around and wondered if Henry was going to walk in outta the snow. I was up to 32,768 times two is the end of the human race …