Numbers whose base-10 representation has the same nonzero number of 0's and 4's.

Terms

a(0) =40a(1) =104a(2) =140a(3) =204a(4) =240a(5) =304a(6) =340a(7) =401a(8) =402a(9) =403a(10) =405a(11) =406a(12) =407a(13) =408a(14) =409a(15) =410a(16) =420a(17) =430a(18) =450a(19) =460a(20) =470a(21) =480a(22) =490a(23) =504a(24) =540a(25) =604a(26) =640a(27) =704a(28) =740a(29) =804