a(n) = n_{2^n}.

Terms

a(0) =1a(1) =2a(2) =3a(3) =4a(4) =5a(5) =6a(6) =7a(7) =8a(8) =9a(9) =1024a(10) =2049a(11) =4098a(12) =8195a(13) =16388a(14) =32773a(15) =65542a(16) =131079a(17) =262152a(18) =524297a(19) =2097152a(20) =4194305a(21) =8388610a(22) =16777219a(23) =33554436a(24) =67108869a(25) =134217734a(26) =268435463a(27) =536870920a(28) =1073741833a(29) =3221225472