Calls frequently does not leave a mssge, who is this??

Called my mobile and left no message.

I've been getting a call from this number about once per week for the past 4 weeks. They do not leave a message. I finally was available to answer the phone just now to see who it is. There was silence, and then the phone hung up. My phone tells me the call is from Las Vegas, Nevada. Seeing as how I was there not too long ago, I thought it was strange and would attempt to pick it up. . . but conducting a search on-line, it seems that this number has been calling many and not leaving a message. . .so finding it strange.