Primes formed by concatenating n, n, n, and 1 for n = 1, 2, 3,....

Terms

a(0) =2221a(1) =3331a(2) =4441a(3) =6661a(4) =1212121a(5) =1616161a(6) =2323231a(7) =2424241a(8) =2828281a(9) =3131311a(10) =3232321a(11) =3333331a(12) =3636361a(13) =3838381a(14) =4040401a(15) =4242421a(16) =4545451a(17) =5454541a(18) =5858581a(19) =6262621a(20) =6868681a(21) =6969691a(22) =7171711a(23) =7272721a(24) =8282821a(25) =9090901a(26) =9999991a(27) =1161161161