A143967 - OEIS

A143967 as a simple table

n	a(n)
1	3
2	7
3	33
4	37
5	73
6	77
7	333
8	337
9	373
10	377
11	733
12	737
13	773
14	777
15	3333
16	3337
17	3373
18	3377
19	3733
20	3737
21	3773
22	3777
23	7333
24	7337
25	7373
26	7377
27	7733
28	7737
29	7773
30	7777
31	33333
32	33337
33	33373
34	33377
35	33733
36	33737
37	33773
38	33777
39	37333
40	37337
41	37373
42	37377

[3,7,33,37,73,77,333,337,373,377,733,737,773,777, 3333,3337,3373,3377,3733,3737,3773,3777,7333,7337, 7373,7377,7733,7737,7773,7777,33333,33337,33373, 33377,33733,33737,33773,33777,37333,37337,37373, 37377]