a(1) = 4; a(n) is smallest number >= a(n-1) such that the juxtaposition a(1)a(2)...a(n) is a prime.

Terms

a(0) =4a(1) =7a(2) =9a(3) =9a(4) =39a(5) =47a(6) =57a(7) =81a(8) =111a(9) =123a(10) =243a(11) =283a(12) =287a(13) =313a(14) =407a(15) =507a(16) =807a(17) =1057a(18) =1209a(19) =1211a(20) =1443a(21) =1447a(22) =1619a(23) =2019a(24) =2269a(25) =2429a(26) =2637a(27) =2679a(28) =2751a(29) =3007