Find how many alphanumeric characters can be made up of a single number
05AB1E, 8 7 bytes

žKÇIŒÃg


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Explanation

žK       # push [a-zA-Z0-9]
  Ç      # convert to list of ascii codes
   IŒ    # push all substrings of input
     Ã   # keep only the subtrings which exist in the list of acsii codes
      g  # push length of resulting list