Simple question...#'s as instances?

i tried using a number (i.e 1487) as a movie clip’s instance but when i tested the movie it said there was an actionscript error. so i changed the instance to letters (i.e. caprese) and it worked fine. (by the way, the actionscript is just for a simple button…
on(release){
1487.gotoAndPlay():
}
can you not use numbers for the instances???
emily