A075610 - cp's OEIS frontend

A075610 a(1) = 1, a(n) = smallest prime number not occurring earlier such that the concatenation a(n-1) and a(n) is a composite number.

n	a(n)
1	1
2	2
3	5
4	7
5	11
6	13
7	3
8	19
9	17
10	29
11	23
12	31
13	41
14	37
15	43
16	47
17	53
18	59
19	61
20	67
21	71
22	73
23	79
24	83
25	97
26	89
27	103
28	101
29	109
30	107
31	113
32	127
33	131
34	137
35	139
36	149
37	151
38	167
39	157
40	173
41	163
42	179
43	181
44	191
45	193
46	197
47	199
48	223
49	227
50	211
51	233
52	229
53	239
54	241
55	251
56	269
57	263
58	271
59	257
60	277

[1, 2, 5, 7, 11, 13, 3, 19, 17, 29, 23, 31, 41, 37, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 97, 89, 103, 101, 109, 107, 113, 127, 131, 137, 139, 149, 151, 167, 157, 173, 163, 179, 181, 191, 193, 197, 199, 223, 227, 211, 233, 229, 239, 241, 251, 269, 263, 271, 257, 277]

cp's OEIS Frontend

A075610 a(1) = 1, a(n) = smallest prime number not occurring earlier such that the concatenation a(n-1) and a(n) is a composite number.

Table of values

List of values

n	a(n)
1	1
2	2
3	5
4	7
5	11
6	13
7	3
8	19
9	17
10	29
11	23
12	31
13	41
14	37
15	43
16	47
17	53
18	59
19	61
20	67
21	71
22	73
23	79
24	83
25	97
26	89
27	103
28	101
29	109
30	107
31	113
32	127
33	131
34	137
35	139
36	149
37	151
38	167
39	157
40	173
41	163
42	179
43	181
44	191
45	193
46	197
47	199
48	223
49	227
50	211
51	233
52	229
53	239
54	241
55	251
56	269
57	263
58	271
59	257
60	277

n	a(n)
1	1
2	2
3	5
4	7
5	11
6	13
7	3
8	19
9	17
10	29
11	23
12	31
13	41
14	37
15	43
16	47
17	53
18	59
19	61
20	67
21	71
22	73
23	79
24	83
25	97
26	89
27	103
28	101
29	109
30	107
31	113
32	127
33	131
34	137
35	139
36	149
37	151
38	167
39	157
40	173
41	163
42	179
43	181
44	191
45	193
46	197
47	199
48	223
49	227
50	211
51	233
52	229
53	239
54	241
55	251
56	269
57	263
58	271
59	257
60	277

n	a(n)
1	1
2	2
3	5
4	7
5	11
6	13
7	3
8	19
9	17
10	29
11	23
12	31
13	41
14	37
15	43
16	47
17	53
18	59
19	61
20	67
21	71
22	73
23	79
24	83
25	97
26	89
27	103
28	101
29	109
30	107
31	113
32	127
33	131
34	137
35	139
36	149
37	151
38	167
39	157
40	173
41	163
42	179
43	181
44	191
45	193
46	197
47	199
48	223
49	227
50	211
51	233
52	229
53	239
54	241
55	251
56	269
57	263
58	271
59	257
60	277