Question 1174673
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Assuming the letters are chosen from a 26-character alphabet, the word "numbers" in the stem of the question actually means "digits", and zero is included in the list of digits, then


a.  *[tex \LARGE 26^4\,\times\,10^3]


																
John
*[tex \LARGE e^{i\pi}\ +\ 1\ =\ 0]
My calculator said it, I believe it, that settles it
*[illustration darwinfish.jpg]

From <https://www.algebra.com/cgi-bin/upload-illustration.mpl> 
I > Ø
*[tex \Large \ \
*[tex \LARGE \ \ \ \ \ \ \ \ \ \  
								
{{n}\choose{r}}
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