A373998 - cp's OEIS frontend

A373998 a(1) = 1, a(2) = 2, a(3) = 3, a(4) = 5; for n > 4, a(n) is the smallest unused positive number that is coprime to a(n-1) and a(n-2) but has a common factor with at least one of a(1)...a(n-3).

n	a(n)
1	1
2	2
3	3
4	5
5	4
6	9
7	25
8	8
9	21
10	55
11	16
12	7
13	11
14	6
15	35
16	121
17	12
18	49
19	65
20	18
21	77
22	13
23	10
24	27
25	91
26	20
27	33
28	119
29	26
30	15
31	17
32	14
33	39
34	85
35	22
36	57
37	115
38	28
39	19
40	23
41	24
42	95
43	143
44	32
45	45
46	133
47	34
48	69
49	125
50	38
51	51
52	145
53	44
54	63
55	29
56	40
57	81
58	161
59	50
60	87
61	169
62	46
63	75
64	187
65	52
66	93
67	175
68	58
69	31
70	99
71	56
72	155

[1, 2, 3, 5, 4, 9, 25, 8, 21, 55, 16, 7, 11, 6, 35, 121, 12, 49, 65, 18, 77, 13, 10, 27, 91, 20, 33, 119, 26, 15, 17, 14, 39, 85, 22, 57, 115, 28, 19, 23, 24, 95, 143, 32, 45, 133, 34, 69, 125, 38, 51, 145, 44, 63, 29, 40, 81, 161, 50, 87, 169, 46, 75, 187, 52, 93, 175, 58, 31, 99, 56, 155]

cp's OEIS Frontend

A373998 a(1) = 1, a(2) = 2, a(3) = 3, a(4) = 5; for n > 4, a(n) is the smallest unused positive number that is coprime to a(n-1) and a(n-2) but has a common factor with at least one of a(1)...a(n-3).

Table of values

List of values

n	a(n)
1	1
2	2
3	3
4	5
5	4
6	9
7	25
8	8
9	21
10	55
11	16
12	7
13	11
14	6
15	35
16	121
17	12
18	49
19	65
20	18
21	77
22	13
23	10
24	27
25	91
26	20
27	33
28	119
29	26
30	15
31	17
32	14
33	39
34	85
35	22
36	57
37	115
38	28
39	19
40	23
41	24
42	95
43	143
44	32
45	45
46	133
47	34
48	69
49	125
50	38
51	51
52	145
53	44
54	63
55	29
56	40
57	81
58	161
59	50
60	87
61	169
62	46
63	75
64	187
65	52
66	93
67	175
68	58
69	31
70	99
71	56
72	155

n	a(n)
1	1
2	2
3	3
4	5
5	4
6	9
7	25
8	8
9	21
10	55
11	16
12	7
13	11
14	6
15	35
16	121
17	12
18	49
19	65
20	18
21	77
22	13
23	10
24	27
25	91
26	20
27	33
28	119
29	26
30	15
31	17
32	14
33	39
34	85
35	22
36	57
37	115
38	28
39	19
40	23
41	24
42	95
43	143
44	32
45	45
46	133
47	34
48	69
49	125
50	38
51	51
52	145
53	44
54	63
55	29
56	40
57	81
58	161
59	50
60	87
61	169
62	46
63	75
64	187
65	52
66	93
67	175
68	58
69	31
70	99
71	56
72	155

n	a(n)
1	1
2	2
3	3
4	5
5	4
6	9
7	25
8	8
9	21
10	55
11	16
12	7
13	11
14	6
15	35
16	121
17	12
18	49
19	65
20	18
21	77
22	13
23	10
24	27
25	91
26	20
27	33
28	119
29	26
30	15
31	17
32	14
33	39
34	85
35	22
36	57
37	115
38	28
39	19
40	23
41	24
42	95
43	143
44	32
45	45
46	133
47	34
48	69
49	125
50	38
51	51
52	145
53	44
54	63
55	29
56	40
57	81
58	161
59	50
60	87
61	169
62	46
63	75
64	187
65	52
66	93
67	175
68	58
69	31
70	99
71	56
72	155