A249802 - cp's OEIS frontend

A249802 a(n) is the smallest prime q such that n(q-1)-1 is prime, that is, the smallest prime q so that n = (p+1)/(q-1) with p prime; or a(n) = -1 if no such q exists.

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

[5, 3, 2, 2, 5, 2, 3, 2, 3, 3, 5, 2, 19, 2, 3, 3, 5, 2, 3, 2, 3, 3, 7, 2, 7, 5, 3, 7, 7, 2, 3, 2, 5, 3, 5, 3, 3, 2, 7, 3, 5, 2, 7, 2, 3, 19, 7, 2, 3, 5, 3, 3, 5, 2, 3, 5, 3, 7, 7, 2, 19, 2, 5, 3, 7, 3, 7, 2, 3, 3, 5, 2, 67, 2, 3, 3, 5, 5, 3, 2, 11, 3, 5, 2, 7, 11]

cp's OEIS Frontend

A249802 a(n) is the smallest prime q such that n(q-1)-1 is prime, that is, the smallest prime q so that n = (p+1)/(q-1) with p prime; or a(n) = -1 if no such q exists.

Table of values

List of values

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

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

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