A387080 - cp's OEIS frontend

A387080 a(1)=1, a(2)=3; thereafter a(n) is either the greatest number k < a(n-1) not already used such that gcd(k, a(n-1)) > 1, or if no such k exists then a(n) is the smallest number k > a(n-1) not already used such that gcd(k, a(n-1)) > 1.

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

[1, 3, 6, 4, 2, 8, 10, 5, 15, 12, 9, 18, 16, 14, 7, 21, 24, 22, 20, 25, 30, 28, 26, 13, 39, 36, 34, 32, 38, 19, 57, 54, 52, 50, 48, 46, 44, 42, 40, 35, 45, 33, 27, 51, 17, 68, 66, 64, 62, 60, 58, 56, 49, 63, 69, 23, 92, 90, 88, 86, 84, 82, 80, 78, 76, 74, 72, 70]

cp's OEIS Frontend

A387080 a(1)=1, a(2)=3; thereafter a(n) is either the greatest number k < a(n-1) not already used such that gcd(k, a(n-1)) > 1, or if no such k exists then a(n) is the smallest number k > a(n-1) not already used such that gcd(k, a(n-1)) > 1.

Table of values

List of values

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

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

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