Macbook Air A1466 - WiFi channel 13
First open you About this Mac - more Info - System Information

then look under the 

WiFi

Here is what it looks in my place in Spain.



The Ch 1..13 are on 2.4 GHz and the 36...140 are on 5GHz, if your router supports it switch to 5 GHz and you will be lonely there (almost)

If not possible to use 5GHz - (router limitation)

Take Note of 

Locale and Country Code (those need to changed to see the Ch 13)

Next check your router settings for Location/Country Code.

The country code of your router is whichever one it was legally purchased for use in. See if it can be changed.