A289994 - cp's OEIS frontend

A289994 a(1) = 1, a(2) = 2, a(n) = smallest number not occurring earlier such that the concatenation a(n-2), a(n-1) and a(n) is a prime.

n	a(n)
1	1
2	2
3	7
4	11
5	19
6	13
7	9
8	21
9	43
10	3
11	31
12	49
13	17
14	37
15	29
16	41
17	27
18	39
19	67
20	33
21	81
22	53
23	51
24	23
25	89
26	91
27	59
28	47
29	73
30	61
31	87
32	99
33	79
34	63
35	117
36	113
37	77
38	127
39	103
40	93
41	111
42	71
43	69
44	101
45	147
46	57
47	97
48	133
49	119
50	121
51	139
52	131
53	107
54	157
55	151
56	123
57	153
58	83
59	143
60	169
61	109
62	137

[1, 2, 7, 11, 19, 13, 9, 21, 43, 3, 31, 49, 17, 37, 29, 41, 27, 39, 67, 33, 81, 53, 51, 23, 89, 91, 59, 47, 73, 61, 87, 99, 79, 63, 117, 113, 77, 127, 103, 93, 111, 71, 69, 101, 147, 57, 97, 133, 119, 121, 139, 131, 107, 157, 151, 123, 153, 83, 143, 169, 109, 137]

cp's OEIS Frontend

A289994 a(1) = 1, a(2) = 2, a(n) = smallest number not occurring earlier such that the concatenation a(n-2), a(n-1) and a(n) is a prime.

Table of values

List of values

n	a(n)
1	1
2	2
3	7
4	11
5	19
6	13
7	9
8	21
9	43
10	3
11	31
12	49
13	17
14	37
15	29
16	41
17	27
18	39
19	67
20	33
21	81
22	53
23	51
24	23
25	89
26	91
27	59
28	47
29	73
30	61
31	87
32	99
33	79
34	63
35	117
36	113
37	77
38	127
39	103
40	93
41	111
42	71
43	69
44	101
45	147
46	57
47	97
48	133
49	119
50	121
51	139
52	131
53	107
54	157
55	151
56	123
57	153
58	83
59	143
60	169
61	109
62	137

n	a(n)
1	1
2	2
3	7
4	11
5	19
6	13
7	9
8	21
9	43
10	3
11	31
12	49
13	17
14	37
15	29
16	41
17	27
18	39
19	67
20	33
21	81
22	53
23	51
24	23
25	89
26	91
27	59
28	47
29	73
30	61
31	87
32	99
33	79
34	63
35	117
36	113
37	77
38	127
39	103
40	93
41	111
42	71
43	69
44	101
45	147
46	57
47	97
48	133
49	119
50	121
51	139
52	131
53	107
54	157
55	151
56	123
57	153
58	83
59	143
60	169
61	109
62	137

n	a(n)
1	1
2	2
3	7
4	11
5	19
6	13
7	9
8	21
9	43
10	3
11	31
12	49
13	17
14	37
15	29
16	41
17	27
18	39
19	67
20	33
21	81
22	53
23	51
24	23
25	89
26	91
27	59
28	47
29	73
30	61
31	87
32	99
33	79
34	63
35	117
36	113
37	77
38	127
39	103
40	93
41	111
42	71
43	69
44	101
45	147
46	57
47	97
48	133
49	119
50	121
51	139
52	131
53	107
54	157
55	151
56	123
57	153
58	83
59	143
60	169
61	109
62	137