A339671 - cp's OEIS frontend

A339671 a(1) = 1, a(2) = 2; for n>2, a(n) = smallest number not already used that shares a prime factor with a(n-1) and has a prime factor not in a(n-2).

n	a(n)
1	1
2	2
3	4
4	6
5	3
6	15
7	5
8	10
9	8
10	12
11	9
12	21
13	7
14	14
15	16
16	18
17	20
18	22
19	11
20	33
21	24
22	26
23	13
24	39
25	27
26	30
27	25
28	35
29	28
30	32
31	34
32	17
33	51
34	36
35	38
36	19
37	57
38	42
39	40
40	44
41	46
42	23
43	69
44	45
45	48
46	50
47	52
48	54
49	56
50	49
51	63
52	60
53	55
54	65
55	70
56	58
57	29
58	87
59	66
60	62
61	31
62	93
63	72
64	64
65	68
66	74
67	37
68	111
69	75
70	78
71	76
72	80
73	82
74	41
75	123
76	81

[1, 2, 4, 6, 3, 15, 5, 10, 8, 12, 9, 21, 7, 14, 16, 18, 20, 22, 11, 33, 24, 26, 13, 39, 27, 30, 25, 35, 28, 32, 34, 17, 51, 36, 38, 19, 57, 42, 40, 44, 46, 23, 69, 45, 48, 50, 52, 54, 56, 49, 63, 60, 55, 65, 70, 58, 29, 87, 66, 62, 31, 93, 72, 64, 68, 74, 37, 111, 75, 78, 76, 80, 82, 41, 123, 81]

cp's OEIS Frontend

A339671 a(1) = 1, a(2) = 2; for n>2, a(n) = smallest number not already used that shares a prime factor with a(n-1) and has a prime factor not in a(n-2).

Table of values

List of values

n	a(n)
1	1
2	2
3	4
4	6
5	3
6	15
7	5
8	10
9	8
10	12
11	9
12	21
13	7
14	14
15	16
16	18
17	20
18	22
19	11
20	33
21	24
22	26
23	13
24	39
25	27
26	30
27	25
28	35
29	28
30	32
31	34
32	17
33	51
34	36
35	38
36	19
37	57
38	42
39	40
40	44
41	46
42	23
43	69
44	45
45	48
46	50
47	52
48	54
49	56
50	49
51	63
52	60
53	55
54	65
55	70
56	58
57	29
58	87
59	66
60	62
61	31
62	93
63	72
64	64
65	68
66	74
67	37
68	111
69	75
70	78
71	76
72	80
73	82
74	41
75	123
76	81

n	a(n)
1	1
2	2
3	4
4	6
5	3
6	15
7	5
8	10
9	8
10	12
11	9
12	21
13	7
14	14
15	16
16	18
17	20
18	22
19	11
20	33
21	24
22	26
23	13
24	39
25	27
26	30
27	25
28	35
29	28
30	32
31	34
32	17
33	51
34	36
35	38
36	19
37	57
38	42
39	40
40	44
41	46
42	23
43	69
44	45
45	48
46	50
47	52
48	54
49	56
50	49
51	63
52	60
53	55
54	65
55	70
56	58
57	29
58	87
59	66
60	62
61	31
62	93
63	72
64	64
65	68
66	74
67	37
68	111
69	75
70	78
71	76
72	80
73	82
74	41
75	123
76	81

n	a(n)
1	1
2	2
3	4
4	6
5	3
6	15
7	5
8	10
9	8
10	12
11	9
12	21
13	7
14	14
15	16
16	18
17	20
18	22
19	11
20	33
21	24
22	26
23	13
24	39
25	27
26	30
27	25
28	35
29	28
30	32
31	34
32	17
33	51
34	36
35	38
36	19
37	57
38	42
39	40
40	44
41	46
42	23
43	69
44	45
45	48
46	50
47	52
48	54
49	56
50	49
51	63
52	60
53	55
54	65
55	70
56	58
57	29
58	87
59	66
60	62
61	31
62	93
63	72
64	64
65	68
66	74
67	37
68	111
69	75
70	78
71	76
72	80
73	82
74	41
75	123
76	81