Well, you are right about 7 having something(OK, quite a bit) to do with Christianity. God created the world in 7 days. Many of Israel's laws of festivals and such had to do with 7. Every 7th year was called Jubilee, and was somewhat like a year off; similar to the 7 days of the week where the Sabbath was a holiday. Noah was required to take 2 of all animals on the Ark
except those that were clean. There were to be 7 of all clean animals on the Ark. (That's a little know fact, but it is in the Bible.
) Seven was considered to be a Holy number, the perfect number, the number of God if you will. That's also why 666 is evil. It's saying that Satan tried to come up to God's standard three times, but fell short each time.
I believe 12 is in the Bible frequently also. Like 12 Tribes of Israel and 12 Disciples. I'm not sure about 3 and 9 though. Hmm... I'll have to go look at that.