A000720 - cp's OEIS frontend

A000720 pi(n), the number of primes <= n. Sometimes called PrimePi(n) to distinguish it from the number 3.14159...

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

[0, 1, 2, 2, 3, 3, 4, 4, 4, 4, 5, 5, 6, 6, 6, 6, 7, 7, 8, 8, 8, 8, 9, 9, 9, 9, 9, 9, 10, 10, 11, 11, 11, 11, 11, 11, 12, 12, 12, 12, 13, 13, 14, 14, 14, 14, 15, 15, 15, 15, 15, 15, 16, 16, 16, 16, 16, 16, 17, 17, 18, 18, 18, 18, 18, 18, 19, 19, 19, 19, 20, 20, 21, 21, 21, 21, 21, 21]

cp's OEIS Frontend

A000720 pi(n), the number of primes <= n. Sometimes called PrimePi(n) to distinguish it from the number 3.14159...

Table of values

List of values

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

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

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