A245441 - cp's OEIS frontend

A245441 a(1)=3, then a(n) = smallest odd k > Ceiling(a(n-1)/2) such that k*2^n-1 is prime.

n	a(n)
1	3
2	3
3	3
4	3
5	7
6	17
7	13
8	27
9	25
10	15
11	25
12	23
13	21
14	15
15	9
16	17
17	15
18	21
19	51
20	35
21	19
22	33
23	25
24	39
25	57
26	57
27	81
28	45
29	45
30	213
31	111
32	57
33	31
34	131
35	99
36	83
37	45
38	27
39	25
40	107
41	55
42	33
43	33
44	35
45	67
46	141
47	91
48	89
49	69
50	41
51	129
52	89
53	147
54	101
55	195
56	129
57	79
58	77
59	45
60	77
61	69
62	53
63	61

[3, 3, 3, 3, 7, 17, 13, 27, 25, 15, 25, 23, 21, 15, 9, 17, 15, 21, 51, 35, 19, 33, 25, 39, 57, 57, 81, 45, 45, 213, 111, 57, 31, 131, 99, 83, 45, 27, 25, 107, 55, 33, 33, 35, 67, 141, 91, 89, 69, 41, 129, 89, 147, 101, 195, 129, 79, 77, 45, 77, 69, 53, 61]

cp's OEIS Frontend

A245441 a(1)=3, then a(n) = smallest odd k > Ceiling(a(n-1)/2) such that k*2^n-1 is prime.

Table of values

List of values

n	a(n)
1	3
2	3
3	3
4	3
5	7
6	17
7	13
8	27
9	25
10	15
11	25
12	23
13	21
14	15
15	9
16	17
17	15
18	21
19	51
20	35
21	19
22	33
23	25
24	39
25	57
26	57
27	81
28	45
29	45
30	213
31	111
32	57
33	31
34	131
35	99
36	83
37	45
38	27
39	25
40	107
41	55
42	33
43	33
44	35
45	67
46	141
47	91
48	89
49	69
50	41
51	129
52	89
53	147
54	101
55	195
56	129
57	79
58	77
59	45
60	77
61	69
62	53
63	61

n	a(n)
1	3
2	3
3	3
4	3
5	7
6	17
7	13
8	27
9	25
10	15
11	25
12	23
13	21
14	15
15	9
16	17
17	15
18	21
19	51
20	35
21	19
22	33
23	25
24	39
25	57
26	57
27	81
28	45
29	45
30	213
31	111
32	57
33	31
34	131
35	99
36	83
37	45
38	27
39	25
40	107
41	55
42	33
43	33
44	35
45	67
46	141
47	91
48	89
49	69
50	41
51	129
52	89
53	147
54	101
55	195
56	129
57	79
58	77
59	45
60	77
61	69
62	53
63	61

n	a(n)
1	3
2	3
3	3
4	3
5	7
6	17
7	13
8	27
9	25
10	15
11	25
12	23
13	21
14	15
15	9
16	17
17	15
18	21
19	51
20	35
21	19
22	33
23	25
24	39
25	57
26	57
27	81
28	45
29	45
30	213
31	111
32	57
33	31
34	131
35	99
36	83
37	45
38	27
39	25
40	107
41	55
42	33
43	33
44	35
45	67
46	141
47	91
48	89
49	69
50	41
51	129
52	89
53	147
54	101
55	195
56	129
57	79
58	77
59	45
60	77
61	69
62	53
63	61