A251554 - cp's OEIS frontend

A251554 a(1)=1, a(2)=2, a(3)=5; 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	2
3	5
4	4
5	15
6	8
7	3
8	10
9	9
10	14
11	27
12	7
13	6
14	35
15	12
16	25
17	16
18	45
19	22
20	21
21	11
22	18
23	55
24	24
25	65
26	28
27	13
28	20
29	39
30	32
31	33
32	26
33	51
34	38
35	17
36	19
37	34
38	57
39	40
40	63
41	44
42	49
43	30
44	77
45	36
46	91
47	46
48	105
49	23
50	42
51	115
52	48
53	85
54	52
55	75
56	56
57	69
58	50
59	81
60	58
61	93
62	29
63	31
64	87
65	62
66	99
67	64
68	111

[1, 2, 5, 4, 15, 8, 3, 10, 9, 14, 27, 7, 6, 35, 12, 25, 16, 45, 22, 21, 11, 18, 55, 24, 65, 28, 13, 20, 39, 32, 33, 26, 51, 38, 17, 19, 34, 57, 40, 63, 44, 49, 30, 77, 36, 91, 46, 105, 23, 42, 115, 48, 85, 52, 75, 56, 69, 50, 81, 58, 93, 29, 31, 87, 62, 99, 64, 111]

cp's OEIS Frontend

A251554 a(1)=1, a(2)=2, a(3)=5; 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	2
3	5
4	4
5	15
6	8
7	3
8	10
9	9
10	14
11	27
12	7
13	6
14	35
15	12
16	25
17	16
18	45
19	22
20	21
21	11
22	18
23	55
24	24
25	65
26	28
27	13
28	20
29	39
30	32
31	33
32	26
33	51
34	38
35	17
36	19
37	34
38	57
39	40
40	63
41	44
42	49
43	30
44	77
45	36
46	91
47	46
48	105
49	23
50	42
51	115
52	48
53	85
54	52
55	75
56	56
57	69
58	50
59	81
60	58
61	93
62	29
63	31
64	87
65	62
66	99
67	64
68	111

n	a(n)
1	1
2	2
3	5
4	4
5	15
6	8
7	3
8	10
9	9
10	14
11	27
12	7
13	6
14	35
15	12
16	25
17	16
18	45
19	22
20	21
21	11
22	18
23	55
24	24
25	65
26	28
27	13
28	20
29	39
30	32
31	33
32	26
33	51
34	38
35	17
36	19
37	34
38	57
39	40
40	63
41	44
42	49
43	30
44	77
45	36
46	91
47	46
48	105
49	23
50	42
51	115
52	48
53	85
54	52
55	75
56	56
57	69
58	50
59	81
60	58
61	93
62	29
63	31
64	87
65	62
66	99
67	64
68	111

n	a(n)
1	1
2	2
3	5
4	4
5	15
6	8
7	3
8	10
9	9
10	14
11	27
12	7
13	6
14	35
15	12
16	25
17	16
18	45
19	22
20	21
21	11
22	18
23	55
24	24
25	65
26	28
27	13
28	20
29	39
30	32
31	33
32	26
33	51
34	38
35	17
36	19
37	34
38	57
39	40
40	63
41	44
42	49
43	30
44	77
45	36
46	91
47	46
48	105
49	23
50	42
51	115
52	48
53	85
54	52
55	75
56	56
57	69
58	50
59	81
60	58
61	93
62	29
63	31
64	87
65	62
66	99
67	64
68	111