A122280 - cp's OEIS frontend

A122280 a(1) = 1, a(2) = 2; for n >= 3, a(n) = the smallest positive integer not occurring earlier in the sequence such that gcd(a(n-1), a(n)) is a prime.

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

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

cp's OEIS Frontend

A122280 a(1) = 1, a(2) = 2; for n >= 3, a(n) = the smallest positive integer not occurring earlier in the sequence such that gcd(a(n-1), a(n)) is a prime.

Table of values

List of values

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

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

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