Rem,
You wrote: It seems that it would be more mathematically correct if God used numbers that were significant in any number system, such as prime numbers or perfect numbers.
It may seem that way to you but, for whatever reason, it certainly seems that the God of the Bible chose to use the numbers 4, 40 and 400 quite often in scripture. The scriptures themselves give abundant testimony to this fact. The fact that part of this same set of numbers, the number 400, instantly comes to mind of astronomers during every total eclipse of the sun was also not my idea. This fact was pointed out to me by several astronomers themselves as I read news stories they had written on a solar eclipse which occurred several years ago.
You speak disparagingly of "numerology," as well you should. Numerology, much like astrology, is pure superstition and has no demonstrable connection to reality. I do not think that my suggestion that the numbers 4, 40 and 400 may constitute the "signs in the sun, moon and stars" which Jesus spoke of can be fairly compared to mere "numerology." For, since these same numbers appear prominently both in the scriptures and in widely published news articles, whenever the moon fully and precisely covers the sun in the sky to create a total solar eclipse, my contentions have a strong and demonstrable connection to reality.
By the way, trying to determine what may be behind the Bible's abundant use of numbers such as 40 is nothing new for Christians. Neither is it an activity which only "crackpots" engage in. The Church father and philosopher Augustine, writing in about 390 AD made the following comments: "Ignorance of numbers, too, prevents us from understanding things that are set down in scripture in a figurative way. A candid mind, if I may so speak, cannot but be anxious, for example, to ascertain what is meant by the fact that Moses and Elijah, and our Lord Himself, all fasted for forty days."
Mike