Elements of the planar rooted trees sub-operad PRT of TN generated by 01.

Terms

a(0) =1a(1) =12a(2) =122a(3) =123a(4) =1222a(5) =1223a(6) =1232a(7) =1233a(8) =1234a(9) =12222a(10) =12223a(11) =12232a(12) =12233a(13) =12234a(14) =12322a(15) =12323a(16) =12332a(17) =12333a(18) =12334a(19) =12342a(20) =12343a(21) =12344a(22) =12345