A121217 - cp's OEIS frontend

A121217 a(1)=1, a(2)=2, a(3)=3; for n > 3, a(n) is the smallest positive integer which does not occur earlier in the sequence and which is not coprime to a(n-2).

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

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

cp's OEIS Frontend

A121217 a(1)=1, a(2)=2, a(3)=3; for n > 3, a(n) is the smallest positive integer which does not occur earlier in the sequence and which is not coprime to a(n-2).

Table of values

List of values

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

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

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