A234808 - cp's OEIS frontend

A234808 a(n) = |{0 < k < n: p = k + phi(n-k) and 2*n - p are both prime}|, where phi(.) is Euler's totient function.

n	a(n)
1	0
2	1
3	1
4	2
5	2
6	3
7	2
8	0
9	3
10	1
11	2
12	5
13	2
14	1
15	5
16	1
17	2
18	7
19	2
20	1
21	4
22	1
23	2
24	1
25	4
26	1
27	4
28	2
29	4
30	11
31	4
32	2
33	3
34	1
35	5
36	2
37	3
38	2
39	6
40	1
41	5
42	15
43	4
44	2
45	9
46	1
47	6
48	2
49	5
50	4
51	6
52	4
53	4
54	3
55	8
56	3
57	6
58	4
59	7
60	21
61	2
62	4
63	7
64	1
65	7
66	4
67	6
68	4
69	6
70	4
71	8
72	22
73	7
74	3
75	13
76	1
77	10
78	5
79	3
80	5
81	7
82	4
83	9
84	5
85	10
86	5
87	8
88	7
89	7
90	6
91	8
92	5
93	6
94	3
95	8
96	6
97	7
98	4
99	8
100	4

[0, 1, 1, 2, 2, 3, 2, 0, 3, 1, 2, 5, 2, 1, 5, 1, 2, 7, 2, 1, 4, 1, 2, 1, 4, 1, 4, 2, 4, 11, 4, 2, 3, 1, 5, 2, 3, 2, 6, 1, 5, 15, 4, 2, 9, 1, 6, 2, 5, 4, 6, 4, 4, 3, 8, 3, 6, 4, 7, 21, 2, 4, 7, 1, 7, 4, 6, 4, 6, 4, 8, 22, 7, 3, 13, 1, 10, 5, 3, 5, 7, 4, 9, 5, 10, 5, 8, 7, 7, 6, 8, 5, 6, 3, 8, 6, 7, 4, 8, 4]

cp's OEIS Frontend

A234808 a(n) = |{0 < k < n: p = k + phi(n-k) and 2*n - p are both prime}|, where phi(.) is Euler's totient function.

Table of values

List of values

n	a(n)
1	0
2	1
3	1
4	2
5	2
6	3
7	2
8	0
9	3
10	1
11	2
12	5
13	2
14	1
15	5
16	1
17	2
18	7
19	2
20	1
21	4
22	1
23	2
24	1
25	4
26	1
27	4
28	2
29	4
30	11
31	4
32	2
33	3
34	1
35	5
36	2
37	3
38	2
39	6
40	1
41	5
42	15
43	4
44	2
45	9
46	1
47	6
48	2
49	5
50	4
51	6
52	4
53	4
54	3
55	8
56	3
57	6
58	4
59	7
60	21
61	2
62	4
63	7
64	1
65	7
66	4
67	6
68	4
69	6
70	4
71	8
72	22
73	7
74	3
75	13
76	1
77	10
78	5
79	3
80	5
81	7
82	4
83	9
84	5
85	10
86	5
87	8
88	7
89	7
90	6
91	8
92	5
93	6
94	3
95	8
96	6
97	7
98	4
99	8
100	4

n	a(n)
1	0
2	1
3	1
4	2
5	2
6	3
7	2
8	0
9	3
10	1
11	2
12	5
13	2
14	1
15	5
16	1
17	2
18	7
19	2
20	1
21	4
22	1
23	2
24	1
25	4
26	1
27	4
28	2
29	4
30	11
31	4
32	2
33	3
34	1
35	5
36	2
37	3
38	2
39	6
40	1
41	5
42	15
43	4
44	2
45	9
46	1
47	6
48	2
49	5
50	4
51	6
52	4
53	4
54	3
55	8
56	3
57	6
58	4
59	7
60	21
61	2
62	4
63	7
64	1
65	7
66	4
67	6
68	4
69	6
70	4
71	8
72	22
73	7
74	3
75	13
76	1
77	10
78	5
79	3
80	5
81	7
82	4
83	9
84	5
85	10
86	5
87	8
88	7
89	7
90	6
91	8
92	5
93	6
94	3
95	8
96	6
97	7
98	4
99	8
100	4

n	a(n)
1	0
2	1
3	1
4	2
5	2
6	3
7	2
8	0
9	3
10	1
11	2
12	5
13	2
14	1
15	5
16	1
17	2
18	7
19	2
20	1
21	4
22	1
23	2
24	1
25	4
26	1
27	4
28	2
29	4
30	11
31	4
32	2
33	3
34	1
35	5
36	2
37	3
38	2
39	6
40	1
41	5
42	15
43	4
44	2
45	9
46	1
47	6
48	2
49	5
50	4
51	6
52	4
53	4
54	3
55	8
56	3
57	6
58	4
59	7
60	21
61	2
62	4
63	7
64	1
65	7
66	4
67	6
68	4
69	6
70	4
71	8
72	22
73	7
74	3
75	13
76	1
77	10
78	5
79	3
80	5
81	7
82	4
83	9
84	5
85	10
86	5
87	8
88	7
89	7
90	6
91	8
92	5
93	6
94	3
95	8
96	6
97	7
98	4
99	8
100	4