A339670 - cp's OEIS frontend

A339670 a(1) = 2, a(2) = 3; for n>2, a(n) = smallest number not already used that shares a prime factor with a(n-2) and has a prime factor not in a(n-1).

n	a(n)
1	2
2	3
3	4
4	6
5	10
6	9
7	5
8	12
9	15
10	8
11	18
12	14
13	20
14	7
15	16
16	21
17	22
18	24
19	11
20	26
21	33
22	13
23	27
24	39
25	30
26	42
27	25
28	28
29	35
30	32
31	40
32	34
33	36
34	17
35	38
36	51
37	19
38	45
39	57
40	48
41	60
42	44
43	46
44	50
45	23
46	52
47	69
48	54
49	63
50	56
51	66
52	49
53	55
54	70
55	65
56	58
57	75
58	29
59	72
60	87
61	62
62	78
63	31
64	64
65	93
66	68
67	81
68	74
69	84
70	37
71	76
72	111
73	80
74	90
75	82

[2, 3, 4, 6, 10, 9, 5, 12, 15, 8, 18, 14, 20, 7, 16, 21, 22, 24, 11, 26, 33, 13, 27, 39, 30, 42, 25, 28, 35, 32, 40, 34, 36, 17, 38, 51, 19, 45, 57, 48, 60, 44, 46, 50, 23, 52, 69, 54, 63, 56, 66, 49, 55, 70, 65, 58, 75, 29, 72, 87, 62, 78, 31, 64, 93, 68, 81, 74, 84, 37, 76, 111, 80, 90, 82]

cp's OEIS Frontend

A339670 a(1) = 2, a(2) = 3; for n>2, a(n) = smallest number not already used that shares a prime factor with a(n-2) and has a prime factor not in a(n-1).

Table of values

List of values

n	a(n)
1	2
2	3
3	4
4	6
5	10
6	9
7	5
8	12
9	15
10	8
11	18
12	14
13	20
14	7
15	16
16	21
17	22
18	24
19	11
20	26
21	33
22	13
23	27
24	39
25	30
26	42
27	25
28	28
29	35
30	32
31	40
32	34
33	36
34	17
35	38
36	51
37	19
38	45
39	57
40	48
41	60
42	44
43	46
44	50
45	23
46	52
47	69
48	54
49	63
50	56
51	66
52	49
53	55
54	70
55	65
56	58
57	75
58	29
59	72
60	87
61	62
62	78
63	31
64	64
65	93
66	68
67	81
68	74
69	84
70	37
71	76
72	111
73	80
74	90
75	82

n	a(n)
1	2
2	3
3	4
4	6
5	10
6	9
7	5
8	12
9	15
10	8
11	18
12	14
13	20
14	7
15	16
16	21
17	22
18	24
19	11
20	26
21	33
22	13
23	27
24	39
25	30
26	42
27	25
28	28
29	35
30	32
31	40
32	34
33	36
34	17
35	38
36	51
37	19
38	45
39	57
40	48
41	60
42	44
43	46
44	50
45	23
46	52
47	69
48	54
49	63
50	56
51	66
52	49
53	55
54	70
55	65
56	58
57	75
58	29
59	72
60	87
61	62
62	78
63	31
64	64
65	93
66	68
67	81
68	74
69	84
70	37
71	76
72	111
73	80
74	90
75	82

n	a(n)
1	2
2	3
3	4
4	6
5	10
6	9
7	5
8	12
9	15
10	8
11	18
12	14
13	20
14	7
15	16
16	21
17	22
18	24
19	11
20	26
21	33
22	13
23	27
24	39
25	30
26	42
27	25
28	28
29	35
30	32
31	40
32	34
33	36
34	17
35	38
36	51
37	19
38	45
39	57
40	48
41	60
42	44
43	46
44	50
45	23
46	52
47	69
48	54
49	63
50	56
51	66
52	49
53	55
54	70
55	65
56	58
57	75
58	29
59	72
60	87
61	62
62	78
63	31
64	64
65	93
66	68
67	81
68	74
69	84
70	37
71	76
72	111
73	80
74	90
75	82