Number of nonempty subsets of {1..n} whose elements have an even average.

Terms

a(0) =0a(1) =1a(2) =3a(3) =4a(4) =6a(5) =13a(6) =25a(7) =38a(8) =64a(9) =119a(10) =219a(11) =384a(12) =686a(13) =1285a(14) =2405a(15) =4428a(16) =8236a(17) =15569a(18) =29463a(19) =55582a(20) =105326a(21) =200847a(22) =383609a(23) =732744a(24) =1403004a(25) =2694391a(26) =5181663a(27) =9973416a(28) =19226166a(29) =37125547