A090368 - cp's OEIS frontend

A090368 a(1) = 1; for n > 1, smallest divisor > 1 of 2n-1.

n	a(n)
1	1
2	3
3	5
4	7
5	3
6	11
7	13
8	3
9	17
10	19
11	3
12	23
13	5
14	3
15	29
16	31
17	3
18	5
19	37
20	3
21	41
22	43
23	3
24	47
25	7
26	3
27	53
28	5
29	3
30	59
31	61
32	3
33	5
34	67
35	3
36	71
37	73
38	3
39	7
40	79
41	3
42	83
43	5
44	3
45	89
46	7
47	3
48	5
49	97
50	3
51	101
52	103
53	3
54	107
55	109
56	3
57	113
58	5
59	3
60	7
61	11
62	3
63	5
64	127
65	3
66	131
67	7
68	3
69	137
70	139
71	3
72	11
73	5
74	3
75	149
76	151
77	3
78	5
79	157
80	3
81	7

[1, 3, 5, 7, 3, 11, 13, 3, 17, 19, 3, 23, 5, 3, 29, 31, 3, 5, 37, 3, 41, 43, 3, 47, 7, 3, 53, 5, 3, 59, 61, 3, 5, 67, 3, 71, 73, 3, 7, 79, 3, 83, 5, 3, 89, 7, 3, 5, 97, 3, 101, 103, 3, 107, 109, 3, 113, 5, 3, 7, 11, 3, 5, 127, 3, 131, 7, 3, 137, 139, 3, 11, 5, 3, 149, 151, 3, 5, 157, 3, 7]

cp's OEIS Frontend

A090368 a(1) = 1; for n > 1, smallest divisor > 1 of 2n-1.

Table of values

List of values

n	a(n)
1	1
2	3
3	5
4	7
5	3
6	11
7	13
8	3
9	17
10	19
11	3
12	23
13	5
14	3
15	29
16	31
17	3
18	5
19	37
20	3
21	41
22	43
23	3
24	47
25	7
26	3
27	53
28	5
29	3
30	59
31	61
32	3
33	5
34	67
35	3
36	71
37	73
38	3
39	7
40	79
41	3
42	83
43	5
44	3
45	89
46	7
47	3
48	5
49	97
50	3
51	101
52	103
53	3
54	107
55	109
56	3
57	113
58	5
59	3
60	7
61	11
62	3
63	5
64	127
65	3
66	131
67	7
68	3
69	137
70	139
71	3
72	11
73	5
74	3
75	149
76	151
77	3
78	5
79	157
80	3
81	7

n	a(n)
1	1
2	3
3	5
4	7
5	3
6	11
7	13
8	3
9	17
10	19
11	3
12	23
13	5
14	3
15	29
16	31
17	3
18	5
19	37
20	3
21	41
22	43
23	3
24	47
25	7
26	3
27	53
28	5
29	3
30	59
31	61
32	3
33	5
34	67
35	3
36	71
37	73
38	3
39	7
40	79
41	3
42	83
43	5
44	3
45	89
46	7
47	3
48	5
49	97
50	3
51	101
52	103
53	3
54	107
55	109
56	3
57	113
58	5
59	3
60	7
61	11
62	3
63	5
64	127
65	3
66	131
67	7
68	3
69	137
70	139
71	3
72	11
73	5
74	3
75	149
76	151
77	3
78	5
79	157
80	3
81	7

n	a(n)
1	1
2	3
3	5
4	7
5	3
6	11
7	13
8	3
9	17
10	19
11	3
12	23
13	5
14	3
15	29
16	31
17	3
18	5
19	37
20	3
21	41
22	43
23	3
24	47
25	7
26	3
27	53
28	5
29	3
30	59
31	61
32	3
33	5
34	67
35	3
36	71
37	73
38	3
39	7
40	79
41	3
42	83
43	5
44	3
45	89
46	7
47	3
48	5
49	97
50	3
51	101
52	103
53	3
54	107
55	109
56	3
57	113
58	5
59	3
60	7
61	11
62	3
63	5
64	127
65	3
66	131
67	7
68	3
69	137
70	139
71	3
72	11
73	5
74	3
75	149
76	151
77	3
78	5
79	157
80	3
81	7