Numbers m such that exactly half of the a such that 0<a<m and (a,m)=1 satisfy a^(m-1) == 1 (mod m).

Terms

a(0) =4a(1) =6a(2) =15a(3) =91a(4) =703a(5) =1891a(6) =2701a(7) =11305a(8) =12403a(9) =13981a(10) =18721a(11) =23001a(12) =30889a(13) =38503a(14) =39865a(15) =49141a(16) =68101a(17) =79003a(18) =88561a(19) =88831a(20) =91001a(21) =93961a(22) =104653a(23) =107185a(24) =137149a(25) =146611a(26) =152551a(27) =157641a(28) =176149a(29) =188191