Who called from 2131111111

I'm getting called by 213-111-1111 several times a day...  No one ever answers.  How do I stop it from calling?

This number has tried to call my home several times today.  When I answer I hear background noise but no one says anything.

I have been getting calls from this number at various times of the day.  No one answers when I answer.

I have been getting these calls for a couple of months now, with a daily frequency  from 0 to 10 times. I estimate I get 10 attempts per week on 4 of 7 days. That frequency makes me think it is auto-dialed. The one time I answered it there was nobody on the line.
I have read (Wikipedia) that 111-111-1111 is a masked number that is used for telemarketing, perhaps this is another.
Some phones are able to block numbers at the handset, that might be a solution.

i get a call from the number 213-111-1111 at least 2 times a day for about 3 months now. we decided to answer it tonight and they hung up on us. i woild love to know who is doing this, getting very annoying