How many different starting characters are possible in Basic/Expert D&D? Don't say seven.
Let's start by assuming that two otherwise identical characters are "different" if one is a Fighter and the other is a Thief, all other things being identical. Let us also assume two Fighters are "different" if one has 1 hit point max and the other has 2hp. Also, two characters differ if one has a Strength score of 10 and the other has a Str of 11. That one will be a stretch for some people, but when you start to think about monsters that do stat damage even one point can be a big difference.
Furthmore, if one character is Lawful and the other Neutral, they are different. Additionally, a starting Magic-User with a Sleep spell is not the same as one who begins play with Shield. Finally, starting money differentiates characters as well. After all, a starting fighter that can afford platemail and a bow is in a different starting position than one who can barely buy leather and a spear.
By these criteria, I calculate 4.3775 x 10^18 possible starting PCs in Basic D&D. That's 4,377,498,837,804,120,000 or more than 4 quadrillion characters, before we even talk about names or homeland or personality or even starting equipment.
The actual number is higher when you start taking into account bonus languages for high Int score. Using the sample chart of 20 monster languages increases the total by a little more than one order of magnitude, I think.
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