a(n) = number of pairs {x,y} with (x,y > 1) such that x^y (= terms of A072103) has bit length <= n.

Terms

a(0) =0a(1) =0a(2) =1a(3) =3a(4) =7a(5) =10a(6) =18a(7) =25a(8) =35a(9) =50a(10) =69a(11) =94a(12) =132a(13) =178a(14) =244a(15) =334a(16) =460a(17) =629a(18) =869a(19) =1201a(20) =1668a(21) =2314a(22) =3223a(23) =4493a(24) =6280a(25) =8793a(26) =12322a(27) =17288a(28) =24286a(29) =34139