A328686 - cp's OEIS frontend

A328686 Define a map from the primes to the primes by f(p) = (p-1)/2 if that is prime, or else (p+1)/2 if that is prime, and otherwise is undefined. Start with the n-th prime and iterate f until we cannot go any further; a(n) is the number of steps.

n	a(n)
1	0
2	1
3	1
4	2
5	2
6	3
7	0
8	0
9	3
10	0
11	0
12	1
13	0
14	0
15	4
16	0
17	1
18	1
19	0
20	0
21	2
22	0
23	1
24	0
25	0
26	0
27	0
28	1
29	0
30	0
31	0
32	0
33	0
34	0
35	0
36	0
37	1
38	0
39	2
40	0
41	1
42	0
43	0
44	1
45	0
46	0
47	0
48	0
49	1
50	0
51	0
52	0
53	0
54	0
55	0
56	1
57	0
58	0
59	1
60	0
61	0
62	0
63	0
64	0
65	2
66	0
67	0
68	0
69	1
70	0
71	0
72	2
73	0
74	0
75	0
76	1
77	0
78	1
79	0
80	0
81	0
82	1
83	0
84	0
85	0
86	0
87	0
88	1

[0, 1, 1, 2, 2, 3, 0, 0, 3, 0, 0, 1, 0, 0, 4, 0, 1, 1, 0, 0, 2, 0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 2, 0, 1, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 1, 0, 0, 1, 0, 0, 0, 0, 0, 2, 0, 0, 0, 1, 0, 0, 2, 0, 0, 0, 1, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1]

cp's OEIS Frontend

A328686 Define a map from the primes to the primes by f(p) = (p-1)/2 if that is prime, or else (p+1)/2 if that is prime, and otherwise is undefined. Start with the n-th prime and iterate f until we cannot go any further; a(n) is the number of steps.

Table of values

List of values

n	a(n)
1	0
2	1
3	1
4	2
5	2
6	3
7	0
8	0
9	3
10	0
11	0
12	1
13	0
14	0
15	4
16	0
17	1
18	1
19	0
20	0
21	2
22	0
23	1
24	0
25	0
26	0
27	0
28	1
29	0
30	0
31	0
32	0
33	0
34	0
35	0
36	0
37	1
38	0
39	2
40	0
41	1
42	0
43	0
44	1
45	0
46	0
47	0
48	0
49	1
50	0
51	0
52	0
53	0
54	0
55	0
56	1
57	0
58	0
59	1
60	0
61	0
62	0
63	0
64	0
65	2
66	0
67	0
68	0
69	1
70	0
71	0
72	2
73	0
74	0
75	0
76	1
77	0
78	1
79	0
80	0
81	0
82	1
83	0
84	0
85	0
86	0
87	0
88	1

n	a(n)
1	0
2	1
3	1
4	2
5	2
6	3
7	0
8	0
9	3
10	0
11	0
12	1
13	0
14	0
15	4
16	0
17	1
18	1
19	0
20	0
21	2
22	0
23	1
24	0
25	0
26	0
27	0
28	1
29	0
30	0
31	0
32	0
33	0
34	0
35	0
36	0
37	1
38	0
39	2
40	0
41	1
42	0
43	0
44	1
45	0
46	0
47	0
48	0
49	1
50	0
51	0
52	0
53	0
54	0
55	0
56	1
57	0
58	0
59	1
60	0
61	0
62	0
63	0
64	0
65	2
66	0
67	0
68	0
69	1
70	0
71	0
72	2
73	0
74	0
75	0
76	1
77	0
78	1
79	0
80	0
81	0
82	1
83	0
84	0
85	0
86	0
87	0
88	1

n	a(n)
1	0
2	1
3	1
4	2
5	2
6	3
7	0
8	0
9	3
10	0
11	0
12	1
13	0
14	0
15	4
16	0
17	1
18	1
19	0
20	0
21	2
22	0
23	1
24	0
25	0
26	0
27	0
28	1
29	0
30	0
31	0
32	0
33	0
34	0
35	0
36	0
37	1
38	0
39	2
40	0
41	1
42	0
43	0
44	1
45	0
46	0
47	0
48	0
49	1
50	0
51	0
52	0
53	0
54	0
55	0
56	1
57	0
58	0
59	1
60	0
61	0
62	0
63	0
64	0
65	2
66	0
67	0
68	0
69	1
70	0
71	0
72	2
73	0
74	0
75	0
76	1
77	0
78	1
79	0
80	0
81	0
82	1
83	0
84	0
85	0
86	0
87	0
88	1