A026238 - cp's OEIS frontend

A026238 a(n) = j if n is the j-th prime, else a(n) = k if n is the k-th composite.

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

[1, 2, 1, 3, 2, 4, 3, 4, 5, 5, 6, 6, 7, 8, 9, 7, 10, 8, 11, 12, 13, 9, 14, 15, 16, 17, 18, 10, 19, 11, 20, 21, 22, 23, 24, 12, 25, 26, 27, 13, 28, 14, 29, 30, 31, 15, 32, 33, 34, 35, 36, 16, 37, 38, 39, 40, 41, 17, 42, 18, 43, 44, 45, 46, 47, 19]

cp's OEIS Frontend

A026238 a(n) = j if n is the j-th prime, else a(n) = k if n is the k-th composite.

Table of values

List of values

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

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

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