"It repeats every seventeen minutes and eleven seconds," said Lucy. Light bars flickered across the screen. "The sequence is simple." Four. Then two clusters of four. The four clusters. Then four clusters of eight. And eight of eight.

"It keeps doubling," he said.

"Up to 256. Then it runs backward."

"Okay. What else is there?"

- McDevitt, Jack. Cauldron. New York: Ace Books, 2007, p.3.