a(n) = (1/n) * Sum_{d divides n} (-1)^(n+d)*phi(n/d)*2^d.

Terms

a(0) =2a(1) =1a(2) =4a(3) =4a(4) =8a(5) =10a(6) =20a(7) =34a(8) =60a(9) =100a(10) =188a(11) =348a(12) =632a(13) =1162a(14) =2192a(15) =4114a(16) =7712a(17) =14542a(18) =27596a(19) =52480a(20) =99880a(21) =190558a(22) =364724a(23) =699248a(24) =1342184a(25) =2580796a(26) =4971068a(27) =9587560a(28) =18512792a(29) =35790376