7

The number 7 is claimed in a number of religions to be a lucky number. Various myths surround why this number should be considered to be lucky, but it is important to note that the number 7 is particularly "lucky" with 2 dice games, where you try to predict what the total of the 2 dice will be. 7 is the most likely number for the total of the 2 dice. Dice games were particularly popular games prior to the invention of playing cards, and would have been the game of choice as at the formation of Christianity and other religions that today have 7 as a lucky number. Almost certainly, therefore, the number 7 is considered lucky actually because it comes up the most regularly in 2-dice games. Mathematical skill was rarely known, and as such few people would have realised that 7 was in fact the most likely to have appeared and would have been happy to accept that it came up regularly because it was lucky, rather than the reality which was that it was statistically the most likely to appear.

Chances for each dice combination in a 2-dice game:

2 = (1,1) (1 chance)

3 = (1,2), (2,1) (2 chances)

4 = (1,3), (2,2), (3,1) (3 chances)

5 = (1,4), (2,3), (3,2), (4,1) (4 chances)

6 = (1,5), (2,4), (3,3), (4,2), (5,1) (5 chances)

7 = (1,6), (2,5), (3,4), (4,3), (5,2), (6,1) (6 chances)

8 = (2,6), (3,5), (4,4), (5,3), (6,2) (5 chances)

9 = (3,6), (4,5), (5,4), (6,3) (4 chances)

10 = (4,6), (5,5), (6,4) (3 chances)

11 = (5,6), (6,5) (2 chances)

12 = (6,6) (1 chance)

26 combinations total. 6 different combinations get a total of 7. Thus the chances of 7 turning up are 6/26, or 23% of the time. Given that there are 11 total results, the odds would likely be 10:1. Playing it 10 times, you would likely win 2.3 times if you pick 7 every time, which would overall mean that you more than double your money if you go for 7 every time.

By using the number 7 as a "lucky number", or even a spiritual number, priests could have fleeced gamblers (and almost certainly did do this) so as to raise money for their cause, which in turn would have helped to convert people to their cause.