Concatenations C1 and C2 are both prime (see the comment lines).

Terms

a(0) =9a(1) =51a(2) =63a(3) =87a(4) =111a(5) =123a(6) =153a(7) =177a(8) =207a(9) =211a(10) =239a(11) =263a(12) =273a(13) =289a(14) =327a(15) =333a(16) =343a(17) =359a(18) =407a(19) =471a(20) =489a(21) =497a(22) =513a(23) =541a(24) =597a(25) =621a(26) =651a(27) =659a(28) =663a(29) =681