A238643 - cp's OEIS frontend

A238643 Number of primes p <= n such that 2pi(p) - (-1)^n and pn +((-1)^n - 3)/2 are both prime, where pi(x) is the number of primes not exceeding x.

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

[0, 0, 1, 1, 2, 2, 1, 1, 1, 1, 2, 2, 2, 3, 4, 2, 1, 3, 1, 2, 5, 2, 3, 3, 1, 2, 3, 3, 1, 4, 2, 1, 4, 2, 3, 5, 3, 1, 2, 2, 2, 3, 3, 4, 4, 2, 3, 2, 1, 2, 5, 1, 3, 4, 1, 2, 3, 1, 2, 4, 4, 2, 5, 4, 2, 5, 2, 1, 2, 4, 3, 5, 3, 1, 6, 7, 3, 5, 3, 3]

cp's OEIS Frontend

A238643 Number of primes p <= n such that 2pi(p) - (-1)^n and pn +((-1)^n - 3)/2 are both prime, where pi(x) is the number of primes not exceeding x.

Table of values

List of values

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

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

cp's OEIS Frontend

A238643 Number of primes p <= n such that 2*pi(p) - (-1)^n and p*n +((-1)^n - 3)/2 are both prime, where pi(x) is the number of primes not exceeding x.

Table of values

List of values

A238643 Number of primes p <= n such that 2pi(p) - (-1)^n and pn +((-1)^n - 3)/2 are both prime, where pi(x) is the number of primes not exceeding x.

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