A243906 - cp's OEIS frontend

A243906 (Number of semiprimes <= n) - (number of primes <= n).

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

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

cp's OEIS Frontend

A243906 (Number of semiprimes <= n) - (number of primes <= n).

Table of values

List of values

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

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

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