A251555 - cp's OEIS frontend

A251555 a(1)=1, a(2)=3, a(3)=2; thereafter a(n) is the smallest number not occurring earlier having at least one common factor with a(n-2), but none with a(n-1).

n	a(n)
1	1
2	3
3	2
4	9
5	4
6	15
7	8
8	5
9	6
10	25
11	12
12	35
13	16
14	7
15	10
16	21
17	20
18	27
19	14
20	33
21	26
22	11
23	13
24	22
25	39
26	28
27	45
28	32
29	51
30	38
31	17
32	18
33	85
34	24
35	55
36	34
37	65
38	36
39	91
40	30
41	49
42	40
43	63
44	44
45	57
46	46
47	19
48	23
49	76
50	69
51	50
52	81
53	52
54	75
55	56
56	87
57	62
58	29
59	31
60	58
61	93
62	64
63	99
64	68
65	77
66	48
67	119
68	54

[1, 3, 2, 9, 4, 15, 8, 5, 6, 25, 12, 35, 16, 7, 10, 21, 20, 27, 14, 33, 26, 11, 13, 22, 39, 28, 45, 32, 51, 38, 17, 18, 85, 24, 55, 34, 65, 36, 91, 30, 49, 40, 63, 44, 57, 46, 19, 23, 76, 69, 50, 81, 52, 75, 56, 87, 62, 29, 31, 58, 93, 64, 99, 68, 77, 48, 119, 54]

cp's OEIS Frontend

A251555 a(1)=1, a(2)=3, a(3)=2; thereafter a(n) is the smallest number not occurring earlier having at least one common factor with a(n-2), but none with a(n-1).

Table of values

List of values

n	a(n)
1	1
2	3
3	2
4	9
5	4
6	15
7	8
8	5
9	6
10	25
11	12
12	35
13	16
14	7
15	10
16	21
17	20
18	27
19	14
20	33
21	26
22	11
23	13
24	22
25	39
26	28
27	45
28	32
29	51
30	38
31	17
32	18
33	85
34	24
35	55
36	34
37	65
38	36
39	91
40	30
41	49
42	40
43	63
44	44
45	57
46	46
47	19
48	23
49	76
50	69
51	50
52	81
53	52
54	75
55	56
56	87
57	62
58	29
59	31
60	58
61	93
62	64
63	99
64	68
65	77
66	48
67	119
68	54

n	a(n)
1	1
2	3
3	2
4	9
5	4
6	15
7	8
8	5
9	6
10	25
11	12
12	35
13	16
14	7
15	10
16	21
17	20
18	27
19	14
20	33
21	26
22	11
23	13
24	22
25	39
26	28
27	45
28	32
29	51
30	38
31	17
32	18
33	85
34	24
35	55
36	34
37	65
38	36
39	91
40	30
41	49
42	40
43	63
44	44
45	57
46	46
47	19
48	23
49	76
50	69
51	50
52	81
53	52
54	75
55	56
56	87
57	62
58	29
59	31
60	58
61	93
62	64
63	99
64	68
65	77
66	48
67	119
68	54

n	a(n)
1	1
2	3
3	2
4	9
5	4
6	15
7	8
8	5
9	6
10	25
11	12
12	35
13	16
14	7
15	10
16	21
17	20
18	27
19	14
20	33
21	26
22	11
23	13
24	22
25	39
26	28
27	45
28	32
29	51
30	38
31	17
32	18
33	85
34	24
35	55
36	34
37	65
38	36
39	91
40	30
41	49
42	40
43	63
44	44
45	57
46	46
47	19
48	23
49	76
50	69
51	50
52	81
53	52
54	75
55	56
56	87
57	62
58	29
59	31
60	58
61	93
62	64
63	99
64	68
65	77
66	48
67	119
68	54