A378459 - cp's OEIS frontend

A378459 a(n) is the least k such that the concatenation of 2^n-1 and 2^k-1 is prime, or -1 if there is no such k.

n	a(n)
1	1
2	1
3	1
4	1
5	1
6	1
7	3
8	1
9	2
10	13
11	3
12	11
13	5
14	5
15	2
16	1
17	6
18	1
19	3
20	1
21	25
22	5
23	9
24	7
25	6
26	3
27	11
28	3
29	2
30	17
31	2
32	99
33	31
34	15
35	3
36	19
37	6
38	9
39	1
40	1
41	5
42	23
43	9
44	1
45	11
46	15
47	5
48	11
49	26
50	9
51	2
52	35
53	17
54	43
55	17
56	61
57	11
58	21
59	13
60	139
61	3
62	13
63	25
64	17
65	14
66	1
67	2
68	21
69	19
70	9
71	3
72	5
73	6
74	177
75	41
76	39
77	2
78	73
79	22
80	9
81	31
82	3
83	2
84	89
85	179
86	21

[1, 1, 1, 1, 1, 1, 3, 1, 2, 13, 3, 11, 5, 5, 2, 1, 6, 1, 3, 1, 25, 5, 9, 7, 6, 3, 11, 3, 2, 17, 2, 99, 31, 15, 3, 19, 6, 9, 1, 1, 5, 23, 9, 1, 11, 15, 5, 11, 26, 9, 2, 35, 17, 43, 17, 61, 11, 21, 13, 139, 3, 13, 25, 17, 14, 1, 2, 21, 19, 9, 3, 5, 6, 177, 41, 39, 2, 73, 22, 9, 31, 3, 2, 89, 179, 21]

cp's OEIS Frontend

A378459 a(n) is the least k such that the concatenation of 2^n-1 and 2^k-1 is prime, or -1 if there is no such k.

Table of values

List of values

n	a(n)
1	1
2	1
3	1
4	1
5	1
6	1
7	3
8	1
9	2
10	13
11	3
12	11
13	5
14	5
15	2
16	1
17	6
18	1
19	3
20	1
21	25
22	5
23	9
24	7
25	6
26	3
27	11
28	3
29	2
30	17
31	2
32	99
33	31
34	15
35	3
36	19
37	6
38	9
39	1
40	1
41	5
42	23
43	9
44	1
45	11
46	15
47	5
48	11
49	26
50	9
51	2
52	35
53	17
54	43
55	17
56	61
57	11
58	21
59	13
60	139
61	3
62	13
63	25
64	17
65	14
66	1
67	2
68	21
69	19
70	9
71	3
72	5
73	6
74	177
75	41
76	39
77	2
78	73
79	22
80	9
81	31
82	3
83	2
84	89
85	179
86	21

n	a(n)
1	1
2	1
3	1
4	1
5	1
6	1
7	3
8	1
9	2
10	13
11	3
12	11
13	5
14	5
15	2
16	1
17	6
18	1
19	3
20	1
21	25
22	5
23	9
24	7
25	6
26	3
27	11
28	3
29	2
30	17
31	2
32	99
33	31
34	15
35	3
36	19
37	6
38	9
39	1
40	1
41	5
42	23
43	9
44	1
45	11
46	15
47	5
48	11
49	26
50	9
51	2
52	35
53	17
54	43
55	17
56	61
57	11
58	21
59	13
60	139
61	3
62	13
63	25
64	17
65	14
66	1
67	2
68	21
69	19
70	9
71	3
72	5
73	6
74	177
75	41
76	39
77	2
78	73
79	22
80	9
81	31
82	3
83	2
84	89
85	179
86	21

n	a(n)
1	1
2	1
3	1
4	1
5	1
6	1
7	3
8	1
9	2
10	13
11	3
12	11
13	5
14	5
15	2
16	1
17	6
18	1
19	3
20	1
21	25
22	5
23	9
24	7
25	6
26	3
27	11
28	3
29	2
30	17
31	2
32	99
33	31
34	15
35	3
36	19
37	6
38	9
39	1
40	1
41	5
42	23
43	9
44	1
45	11
46	15
47	5
48	11
49	26
50	9
51	2
52	35
53	17
54	43
55	17
56	61
57	11
58	21
59	13
60	139
61	3
62	13
63	25
64	17
65	14
66	1
67	2
68	21
69	19
70	9
71	3
72	5
73	6
74	177
75	41
76	39
77	2
78	73
79	22
80	9
81	31
82	3
83	2
84	89
85	179
86	21