Please identify all the named entities mentioned in the input sentence provided below. Use only the categories: PER - person, ORG - organization, and LOC - location.
Remember, nationalities are neither locations nor organizations, and organizations can represent other groups of people.
Pay attention to the provided example. You should only output the results in JSON format, following a similar structure to the example result provided.

Example sentence and results:

Where in the world is Iguazu?

"Results": [
    {
        "TypeName": "LOC",
        "Text": "Iguazu",
        "Start": 22,
        "End": 28
    }
]

Considering the input sentence below, what is the output result?

The letters, six in all, were sent within two hours of each other and represented dozens of power generators.


"Results": []