The number 7 has always been special. I know from Bible study that 7 is a significant number, the number for completion. When you really pay attention, 7 is used to signify all sorts of things, not just when counting. I wonder if the creator of Boeing numbered all of his planes starting with the number 7 because planes fly through the heavens? Anyway, the relation between 7 and a number of things (pardon the pun) is interesting.
The number 7 appears in the Bible 735 times and 777 is often chosen to represent God. Boeing does have quite an affinity for 7 and their model 777 is a masterpiece of aviation. Then there is also Boeing 7J7, 247, 377, 707, 717, 727, 737, 747, 757, 767, 787 and 2707. I'm glad to know you're intrigued by 7.7: The Magical, Amazing and Popular Number Seven
I thought the connection with the number 7 in various religions was interesting. Among the many connections, Christianity has the 7 gifts of the holy spirit: wisdom, understanding, counsel, fortitude, knowledge, piety, and fear of God. Ancient Jews were guided by the 7 laws of Noah. Islam teaches there are 7 heavens and 7 earths. The number 7 also has special meaning in Buddhism and many other religions.