What do you mean by "inverted the position of two of those words, two times"? How exactly you did that will affect the number of possibilities (as some orderings could be ruled out).
The upper bound to this is (24 choose 4) * 4! = 255024. (24 choose 4) is the number of ways you can choose 4 items from a set of 24 elements. 4! is the number of ways you can order those 4 elements. This is a multiplication since for each way you can choose 4 items, there are 4! ways you can rearrange them.
Let's say the seed is:
Word1 Word2 Word3 Word4 Word5 Word6 Word7 Word8 Word9 Word10 Word11 Word12 Word13 Word14 Word15 Word16 Word17 Word18 Word19 Word20 Word21 Word22 Word23 Word24
Well, my "encryption" technique was to write in that order:
Word1
Word23 Word3
Word21 Word5 Word6 Word7 Word8 Word9 Word10 Word11 Word12 Word13 Word14 Word15 Word16 Word17 Word18 Word19 Word20
Word4 Word22
Word2 Word24
So I switched Word2 <> Word23 and Word21 <> Word4
But when I try to revert that, this doesn't work. So I must have screwed up somewhere. My hypothesis is that I have inverted the "wrong" words, but I don't know which ones.
The inversion should have been made in a symetrical position, like in my example.
But since I screw up, maybe I have switched words in a non symetrical position.
