the sf story that you're alluding to is, I believe, Fred Pohl's "Gold at the Starbow's End" --- a cover story in ANALOG magazine ca. 1968 --- which I remember fondly precisely because of the idea used which you mention, namely, encoding a big message compactly as the sum of various powers of small numbers ... though the author got it pretty badly wrong, as I pointed out in a letter published some months later in the same magazine --- the sum of powers that he gave in the story was *much* too small to hold a significant amount of information, and (worse) he thought that one couldn't get any of the answer without writing the entire number --- obviously wrong, as a little modular arithmetic can get out the powers quite easily.... but it's a nice idea and the story was quite good otherwise.... :-) ^z