code: def letterSequence(letters, w=40):
    
    sequence = []
    for letter in letters:
      i = ord(letter) - ord('A')
      sequence.append(set(range(i*w,(i+1)*w)))
    return sequence
docs: Return a list of input vectors corresponding to sequence of letters.
    The vector for each letter has w contiguous bits ON and represented as a
    sequence of non-zero indices.