IanC is a little confused. Brythonic isd not a term used for pre-Celtic laguages, it is the term used to distinguish Britsaish Celtic languages from Gaelic(or Goidelic) languages. Also, of course the Cumbrian yan/tan counting is connected to Welsh and other British Celktic languages(though it has other elements as well). Just take a look at the Welsh for 1-20.