A049201 If n is not composite, a(n) = n followed by 1; if n is composite, a(n) = concatenation of prime factors of n.

1, 11, 21, 31, 22, 51, 23, 71, 222, 33, 25, 111, 223, 131, 27, 35, 2222, 171, 233, 191, 225, 37, 31, 231, 2223, 55, 33, 333, 227, 291, 235, 311, 22222, 41, 37, 57, 2233, 371, 39, 43, 2225, 411, 237, 431, 231, 335, 43, 471, 22223, 77, 255, 47, 233, 531, 2333, 61