A139637 - cp's OEIS frontend

A139637 If n = the k-th prime, then a(n) = the (k-1)th prime. If n = the k-th composite, then a(n) = the (k-1)th composite. a(2) = 1. a(4) = 0.

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

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

cp's OEIS Frontend

A139637 If n = the k-th prime, then a(n) = the (k-1)th prime. If n = the k-th composite, then a(n) = the (k-1)th composite. a(2) = 1. a(4) = 0.

Table of values

List of values

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

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

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