E stands for the amount of elements, 2 stands for double, 3 stands for triple etc...
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I have calculated how many monsters there would be in an island with each amount of elements! (1-20)
When adding another element, the new doubles would be each of the singles plus that element. So you add the previous amount of doubles + the previous amount of singles to know how many there are next. For triple ls you do the same thing but with the doubles instead of singles, for quads you the same thing but with triples, and for quints you so the same thing but with quads. Make sense?
So there would be a total of 22,323 monsters on a twenty element island. (If it doesn't go past quints.
Hopefully I'm not bad at math and doing this all wrong...