A238570 - cp's OEIS frontend

A238570 a(n) = |{0 < k < n: pi((k+1)^2) - pi(k^2) and pi(n^2) - pi(k^2) are both prime}|, where pi(x) denotes the number of primes not exceeding x.

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

[0, 1, 1, 1, 3, 4, 2, 1, 2, 3, 1, 1, 3, 3, 1, 1, 3, 2, 2, 2, 4, 5, 2, 5, 3, 6, 4, 5, 4, 1, 2, 2, 6, 4, 2, 1, 3, 1, 1, 5, 5, 1, 6, 3, 3, 7, 4, 6, 1, 4, 5, 3, 4, 4, 7, 6, 4, 7, 6, 6, 1, 3, 3, 5, 6, 6, 3, 4, 9, 6, 4, 2, 5, 3, 8, 3, 3, 6, 8, 6]

cp's OEIS Frontend

A238570 a(n) = |{0 < k < n: pi((k+1)^2) - pi(k^2) and pi(n^2) - pi(k^2) are both prime}|, where pi(x) denotes the number of primes not exceeding x.

Table of values

List of values

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

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

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