Numbers k>1 such that 10^phi(k) == 1 (mod k^2), where phi(n)=A000010(n).

Terms

a(0) =3a(1) =487a(2) =1461a(3) =4383a(4) =13149a(5) =39447a(6) =118341a(7) =355023a(8) =56598313a(9) =169794939a(10) =509384817a(11) =1754547703a(12) =5263643109a(13) =7187985751a(14) =15790929327a(15) =21563957253a(16) =27563378431a(17) =33902389487a(18) =47372787981a(19) =50315900257a(20) =64691871759a(21) =82690135293a(22) =101707168461a(23) =150947700771