a(n) = Sum_{i=1..n} 2^phi(i), where phi=A000010.

Terms

a(0) =2a(1) =4a(2) =8a(3) =12a(4) =28a(5) =32a(6) =96a(7) =112a(8) =176a(9) =192a(10) =1216a(11) =1232a(12) =5328a(13) =5392a(14) =5648a(15) =5904a(16) =71440a(17) =71504a(18) =333648a(19) =333904a(20) =338000a(21) =339024a(22) =4533328a(23) =4533584a(24) =5582160a(25) =5586256a(26) =5848400a(27) =5852496a(28) =274287952a(29) =274288208