Lucky numbers that are concatenations of n with n + 4.

Terms

a(0) =15a(1) =37a(2) =1519a(3) =1923a(4) =2125a(5) =3943a(6) =5559a(7) =6367a(8) =7377a(9) =8589a(10) =99103a(11) =111115a(12) =117121a(13) =135139a(14) =159163a(15) =165169a(16) =201205a(17) =219223a(18) =261265a(19) =267271a(20) =273277a(21) =327331a(22) =333337a(23) =345349a(24) =357361a(25) =369373a(26) =381385a(27) =399403a(28) =423427a(29) =471475