Beginning with 2, least number such that concatenation of r copies of a(r), r = 1 to n is prime.

Terms

a(0) =2a(1) =1a(2) =3a(3) =1a(4) =9a(5) =3a(6) =273a(7) =219a(8) =7a(9) =281a(10) =11a(11) =119a(12) =1019a(13) =111a(14) =47a(15) =69a(16) =171a(17) =161a(18) =103a(19) =477a(20) =817a(21) =129a(22) =271a(23) =73a(24) =1867a(25) =381a(26) =507a(27) =113a(28) =2643a(29) =487