A375564 - cp's OEIS frontend

A375564 a(1) = 1, a(2) = 2; for n > 2, a(n) is the smallest unused positive number that is coprime to a(n-1) if a(n-1) is prime, otherwise a(n) shares a factor with a(n-1).

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

[1, 2, 3, 4, 6, 8, 10, 5, 7, 9, 12, 14, 16, 18, 15, 20, 22, 11, 13, 17, 19, 21, 24, 26, 28, 30, 25, 35, 40, 32, 34, 36, 27, 33, 39, 42, 38, 44, 46, 23, 29, 31, 37, 41, 43, 45, 48, 50, 52, 54, 51, 57, 60, 55, 65, 70, 49, 56, 58, 62, 64, 66, 63, 69, 72, 68, 74, 76, 78, 75, 80, 82, 84, 77, 88, 86, 90]

cp's OEIS Frontend

A375564 a(1) = 1, a(2) = 2; for n > 2, a(n) is the smallest unused positive number that is coprime to a(n-1) if a(n-1) is prime, otherwise a(n) shares a factor with a(n-1).

Table of values

List of values

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

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

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