A381873 - cp's OEIS frontend

A381873 a(1) = 1, a(2) = 2; for n > 2, a(n) is the smallest unused positive number that shares a factor with a(n-1) while containing at most two distinct prime factors.

n	a(n)
1	1
2	2
3	4
4	6
5	3
6	9
7	12
8	8
9	10
10	5
11	15
12	18
13	14
14	7
15	21
16	24
17	16
18	20
19	22
20	11
21	33
22	27
23	36
24	26
25	13
26	39
27	45
28	25
29	35
30	28
31	32
32	34
33	17
34	51
35	48
36	38
37	19
38	57
39	54
40	40
41	44
42	46
43	23
44	69
45	63
46	49
47	56
48	50
49	52
50	58
51	29
52	87
53	72
54	62
55	31
56	93
57	75
58	55
59	65
60	80
61	64
62	68
63	74
64	37
65	111
66	81

[1, 2, 4, 6, 3, 9, 12, 8, 10, 5, 15, 18, 14, 7, 21, 24, 16, 20, 22, 11, 33, 27, 36, 26, 13, 39, 45, 25, 35, 28, 32, 34, 17, 51, 48, 38, 19, 57, 54, 40, 44, 46, 23, 69, 63, 49, 56, 50, 52, 58, 29, 87, 72, 62, 31, 93, 75, 55, 65, 80, 64, 68, 74, 37, 111, 81]

cp's OEIS Frontend

A381873 a(1) = 1, a(2) = 2; for n > 2, a(n) is the smallest unused positive number that shares a factor with a(n-1) while containing at most two distinct prime factors.

Table of values

List of values

n	a(n)
1	1
2	2
3	4
4	6
5	3
6	9
7	12
8	8
9	10
10	5
11	15
12	18
13	14
14	7
15	21
16	24
17	16
18	20
19	22
20	11
21	33
22	27
23	36
24	26
25	13
26	39
27	45
28	25
29	35
30	28
31	32
32	34
33	17
34	51
35	48
36	38
37	19
38	57
39	54
40	40
41	44
42	46
43	23
44	69
45	63
46	49
47	56
48	50
49	52
50	58
51	29
52	87
53	72
54	62
55	31
56	93
57	75
58	55
59	65
60	80
61	64
62	68
63	74
64	37
65	111
66	81

n	a(n)
1	1
2	2
3	4
4	6
5	3
6	9
7	12
8	8
9	10
10	5
11	15
12	18
13	14
14	7
15	21
16	24
17	16
18	20
19	22
20	11
21	33
22	27
23	36
24	26
25	13
26	39
27	45
28	25
29	35
30	28
31	32
32	34
33	17
34	51
35	48
36	38
37	19
38	57
39	54
40	40
41	44
42	46
43	23
44	69
45	63
46	49
47	56
48	50
49	52
50	58
51	29
52	87
53	72
54	62
55	31
56	93
57	75
58	55
59	65
60	80
61	64
62	68
63	74
64	37
65	111
66	81

n	a(n)
1	1
2	2
3	4
4	6
5	3
6	9
7	12
8	8
9	10
10	5
11	15
12	18
13	14
14	7
15	21
16	24
17	16
18	20
19	22
20	11
21	33
22	27
23	36
24	26
25	13
26	39
27	45
28	25
29	35
30	28
31	32
32	34
33	17
34	51
35	48
36	38
37	19
38	57
39	54
40	40
41	44
42	46
43	23
44	69
45	63
46	49
47	56
48	50
49	52
50	58
51	29
52	87
53	72
54	62
55	31
56	93
57	75
58	55
59	65
60	80
61	64
62	68
63	74
64	37
65	111
66	81