A083439 - cp's OEIS frontend

A083439 a(1) = 3; then a(n+1) = smallest prime not already in the sequence such that the concatenations a(n)a(n+1) and a(n+1)a(n) are both primes.

n	a(n)
3	3
4	7
5	19
6	13
7	61
8	151
9	31
10	139
11	67
12	37
13	79
14	193
15	163
16	127
17	157
18	97
19	43
20	103
21	307
22	367
23	457
24	643
25	73
26	277
27	223
28	229
29	373
30	199
31	109
32	313
33	211
34	271
35	241
36	421
37	181
38	283
39	397
40	337
41	349
42	331
43	577
44	523
45	463
46	613
47	439
48	541
49	571
50	433
51	787
52	547
53	661
54	769
55	487
56	601
57	823
58	709

[3, 7, 19, 13, 61, 151, 31, 139, 67, 37, 79, 193, 163, 127, 157, 97, 43, 103, 307, 367, 457, 643, 73, 277, 223, 229, 373, 199, 109, 313, 211, 271, 241, 421, 181, 283, 397, 337, 349, 331, 577, 523, 463, 613, 439, 541, 571, 433, 787, 547, 661, 769, 487, 601, 823, 709]

cp's OEIS Frontend

A083439 a(1) = 3; then a(n+1) = smallest prime not already in the sequence such that the concatenations a(n)a(n+1) and a(n+1)a(n) are both primes.

Table of values

List of values

n	a(n)
3	3
4	7
5	19
6	13
7	61
8	151
9	31
10	139
11	67
12	37
13	79
14	193
15	163
16	127
17	157
18	97
19	43
20	103
21	307
22	367
23	457
24	643
25	73
26	277
27	223
28	229
29	373
30	199
31	109
32	313
33	211
34	271
35	241
36	421
37	181
38	283
39	397
40	337
41	349
42	331
43	577
44	523
45	463
46	613
47	439
48	541
49	571
50	433
51	787
52	547
53	661
54	769
55	487
56	601
57	823
58	709

n	a(n)
3	3
4	7
5	19
6	13
7	61
8	151
9	31
10	139
11	67
12	37
13	79
14	193
15	163
16	127
17	157
18	97
19	43
20	103
21	307
22	367
23	457
24	643
25	73
26	277
27	223
28	229
29	373
30	199
31	109
32	313
33	211
34	271
35	241
36	421
37	181
38	283
39	397
40	337
41	349
42	331
43	577
44	523
45	463
46	613
47	439
48	541
49	571
50	433
51	787
52	547
53	661
54	769
55	487
56	601
57	823
58	709

n	a(n)
3	3
4	7
5	19
6	13
7	61
8	151
9	31
10	139
11	67
12	37
13	79
14	193
15	163
16	127
17	157
18	97
19	43
20	103
21	307
22	367
23	457
24	643
25	73
26	277
27	223
28	229
29	373
30	199
31	109
32	313
33	211
34	271
35	241
36	421
37	181
38	283
39	397
40	337
41	349
42	331
43	577
44	523
45	463
46	613
47	439
48	541
49	571
50	433
51	787
52	547
53	661
54	769
55	487
56	601
57	823
58	709