A082462 - cp's OEIS frontend

A082462 Let chi(k) = 1 if prime(k+1) - prime(k) = 2, = 0 otherwise; sequence gives a(n) = sum_{k <= n} chi(k).

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

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

cp's OEIS Frontend

A082462 Let chi(k) = 1 if prime(k+1) - prime(k) = 2, = 0 otherwise; sequence gives a(n) = sum_{k <= n} chi(k).

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