Rock guitar power chord symbol A5 B5 C5.. won't print via \chords { c1:5 }

[Albert Loo]

> I'm not top posting.

\version "2.12.0"

%% Rock guitar power chord A5 B5 C5.. symbol won't print
%% Although I do now use A3 B3 C3.. it won't print either

\chords { 
c1 c1:3 c1:5 c1:7 c1:7+
}