A007931 - OEIS

A007931 as a simple table

n	a(n)
1	1
2	2
3	11
4	12
5	21
6	22
7	111
8	112
9	121
10	122
11	211
12	212
13	221
14	222
15	1111
16	1112
17	1121
18	1122
19	1211
20	1212
21	1221
22	1222
23	2111
24	2112
25	2121
26	2122
27	2211
28	2212
29	2221
30	2222
31	11111
32	11112
33	11121
34	11122
35	11211
36	11212
37	11221
38	11222
39	12111
40	12112
41	12121
42	12122

[1,2,11,12,21,22,111,112,121,122,211,212,221,222, 1111,1112,1121,1122,1211,1212,1221,1222,2111,2112, 2121,2122,2211,2212,2221,2222,11111,11112,11121, 11122,11211,11212,11221,11222,12111,12112,12121, 12122]