Either prank call or telemarketer.  Upon answering the phone, caller did not speak.  If it's a telemarketer they use voice recognition  for the word "hello."  Instead of answering the phone "hello" if caller is unknown, i answer by reciting my phone number.  Another website lists this number as harassment, calling 10 times per day.  Unknown Caller is displayed on the CID.  Time for call blocker.