What is the total number of different 6-letter permutations ("words") that start and end with the same letter and have no other letter repetitions (meaning all the other letters appear only once in "word"). For example AYSDA is one such permutation, but AYSDZ isn't because the start and end are different. And AYSYA and AYADA also are not, because they have other letter repetitions (two Y's for the former and an additional A for the latter).