A075607 - cp's OEIS frontend

A075607 a(1) = 1, a(n) = smallest number not occurring earlier such that the concatenation a(n-1) and a(n) is a prime.

n	a(n)
1	1
2	3
3	7
4	9
5	11
6	17
7	21
8	13
9	19
10	31
11	37
12	27
13	29
14	39
15	23
16	33
17	43
18	49
19	51
20	47
21	59
22	53
23	81
24	61
25	63
26	67
27	79
28	93
29	41
30	57
31	83
32	69
33	71
34	77
35	89
36	99
37	73
38	121
39	97
40	87
41	103
42	91
43	127
44	123
45	113
46	111
47	109
48	133
49	117
50	101
51	107
52	119
53	129
54	169
55	151
56	141
57	131
58	143
59	137
60	147
61	139

[1, 3, 7, 9, 11, 17, 21, 13, 19, 31, 37, 27, 29, 39, 23, 33, 43, 49, 51, 47, 59, 53, 81, 61, 63, 67, 79, 93, 41, 57, 83, 69, 71, 77, 89, 99, 73, 121, 97, 87, 103, 91, 127, 123, 113, 111, 109, 133, 117, 101, 107, 119, 129, 169, 151, 141, 131, 143, 137, 147, 139]

cp's OEIS Frontend

A075607 a(1) = 1, a(n) = smallest number not occurring earlier such that the concatenation a(n-1) and a(n) is a prime.

Table of values

List of values

n	a(n)
1	1
2	3
3	7
4	9
5	11
6	17
7	21
8	13
9	19
10	31
11	37
12	27
13	29
14	39
15	23
16	33
17	43
18	49
19	51
20	47
21	59
22	53
23	81
24	61
25	63
26	67
27	79
28	93
29	41
30	57
31	83
32	69
33	71
34	77
35	89
36	99
37	73
38	121
39	97
40	87
41	103
42	91
43	127
44	123
45	113
46	111
47	109
48	133
49	117
50	101
51	107
52	119
53	129
54	169
55	151
56	141
57	131
58	143
59	137
60	147
61	139

n	a(n)
1	1
2	3
3	7
4	9
5	11
6	17
7	21
8	13
9	19
10	31
11	37
12	27
13	29
14	39
15	23
16	33
17	43
18	49
19	51
20	47
21	59
22	53
23	81
24	61
25	63
26	67
27	79
28	93
29	41
30	57
31	83
32	69
33	71
34	77
35	89
36	99
37	73
38	121
39	97
40	87
41	103
42	91
43	127
44	123
45	113
46	111
47	109
48	133
49	117
50	101
51	107
52	119
53	129
54	169
55	151
56	141
57	131
58	143
59	137
60	147
61	139

n	a(n)
1	1
2	3
3	7
4	9
5	11
6	17
7	21
8	13
9	19
10	31
11	37
12	27
13	29
14	39
15	23
16	33
17	43
18	49
19	51
20	47
21	59
22	53
23	81
24	61
25	63
26	67
27	79
28	93
29	41
30	57
31	83
32	69
33	71
34	77
35	89
36	99
37	73
38	121
39	97
40	87
41	103
42	91
43	127
44	123
45	113
46	111
47	109
48	133
49	117
50	101
51	107
52	119
53	129
54	169
55	151
56	141
57	131
58	143
59	137
60	147
61	139