⑴若α∥β,则l⊥m
⑵若l⊥m,则α∥β
⑶若α⊥β,则l⊥m
⑷若l∥m,则α⊥β
①若{an}是“等方差数列”,则数列{ }是等差数列;
②{(﹣2)n}是“等方差数列”;
③若{an}是“等方差数列”,则数列{akn}(k∈N* , k为常数)也是“等方差数列”;
④若{an}既是“等方差数列”,又是等差数列,则该数列是常数数列.
其中正确命题的个数为( )