Typical staged robocall where they let your phone ring one time. Then, when you look at your missed calls, there is a number. The telemarketers are hoping that you will call them back and that way they will know whether your number is "active" or not. Alternately, they hope you will call them back because then they can show your call coming in and claim that you and they are doing business (why else would you call?) and therefor are an exception to the do not call list.