Half totient of 2^n+1.

Terms

a(0) =1a(1) =2a(2) =3a(3) =8a(4) =10a(5) =24a(6) =42a(7) =128a(8) =162a(9) =400a(10) =682a(11) =1920a(12) =2730a(13) =6272a(14) =9900a(15) =32768a(16) =43690a(17) =93312a(18) =174762a(19) =493440a(20) =682668a(21) =1672704a(22) =2796202a(23) =8257536a(24) =10125000a(25) =26153088a(26) =42384060a(27) =126322560a(28) =175923744a(29) =380160000