A233918 - cp's OEIS frontend

A233918 a(n) = |{0 < k <= n/2: (phi(k) + phi(n-k))/2 is prime}|, where phi(.) is Euler's totient function.

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

[0, 0, 0, 0, 0, 1, 1, 2, 2, 1, 2, 3, 1, 3, 2, 4, 3, 2, 7, 1, 3, 3, 4, 7, 2, 4, 5, 5, 5, 5, 6, 6, 4, 7, 5, 6, 4, 4, 11, 5, 5, 5, 11, 4, 3, 5, 7, 12, 4, 6, 11, 3, 6, 7, 8, 6, 7, 8, 11, 10, 5, 9, 7, 9, 5, 4, 14, 8, 9, 6, 10, 7, 6, 10, 9, 10, 7, 10, 11, 7, 7, 13, 11, 13, 5, 8, 11, 9, 9, 3, 12, 4, 11, 13, 11, 19, 8, 12, 11, 7]

cp's OEIS Frontend

A233918 a(n) = |{0 < k <= n/2: (phi(k) + phi(n-k))/2 is prime}|, where phi(.) is Euler's totient function.

Table of values

List of values

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

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

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