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) =11a(4) =81a(5) =87a(6) =109a(7) =117a(8) =123a(9) =129a(10) =201a(11) =389a(12) =429a(13) =441a(14) =771a(15) =811a(16) =831a(17) =1037a(18) =1143a(19) =1299a(20) =1569a(21) =1581a(22) =1803a(23) =1837a(24) =1943a(25) =2053a(26) =2171a(27) =2379a(28) =2431a(29) =3201