A255509 - cp's OEIS frontend

A255509 a(1)=1, a(2)=2, a(3)=3; for n>=4, a(n) is the maximal prime factor P_n of a(n-2) if P_n is not already a term, otherwise a(n) is the smallest not appeared earlier positive number x such that gcd(x,a(n-2))>1, gcd(x,a(n-1))=1.

n	a(n)
1	1
2	2
3	3
4	4
5	9
6	8
7	15
8	14
9	5
10	7
11	10
12	21
13	16
14	27
15	20
16	33
17	25
18	11
19	30
20	77
21	6
22	35
23	12
24	49
25	18
26	91
27	22
28	13
29	24
30	65
31	28
32	39
33	32
34	45
35	26
36	51
37	38
38	17
39	19
40	34
41	57
42	40
43	63
44	44
45	69
46	50
47	23
48	36
49	115
50	42
51	55
52	46
53	75
54	52
55	81
56	56
57	87
58	62
59	29
60	31
61	58
62	93
63	64
64	99
65	68
66	105
67	74

[1, 2, 3, 4, 9, 8, 15, 14, 5, 7, 10, 21, 16, 27, 20, 33, 25, 11, 30, 77, 6, 35, 12, 49, 18, 91, 22, 13, 24, 65, 28, 39, 32, 45, 26, 51, 38, 17, 19, 34, 57, 40, 63, 44, 69, 50, 23, 36, 115, 42, 55, 46, 75, 52, 81, 56, 87, 62, 29, 31, 58, 93, 64, 99, 68, 105, 74]

cp's OEIS Frontend

A255509 a(1)=1, a(2)=2, a(3)=3; for n>=4, a(n) is the maximal prime factor P_n of a(n-2) if P_n is not already a term, otherwise a(n) is the smallest not appeared earlier positive number x such that gcd(x,a(n-2))>1, gcd(x,a(n-1))=1.

Table of values

List of values

n	a(n)
1	1
2	2
3	3
4	4
5	9
6	8
7	15
8	14
9	5
10	7
11	10
12	21
13	16
14	27
15	20
16	33
17	25
18	11
19	30
20	77
21	6
22	35
23	12
24	49
25	18
26	91
27	22
28	13
29	24
30	65
31	28
32	39
33	32
34	45
35	26
36	51
37	38
38	17
39	19
40	34
41	57
42	40
43	63
44	44
45	69
46	50
47	23
48	36
49	115
50	42
51	55
52	46
53	75
54	52
55	81
56	56
57	87
58	62
59	29
60	31
61	58
62	93
63	64
64	99
65	68
66	105
67	74

n	a(n)
1	1
2	2
3	3
4	4
5	9
6	8
7	15
8	14
9	5
10	7
11	10
12	21
13	16
14	27
15	20
16	33
17	25
18	11
19	30
20	77
21	6
22	35
23	12
24	49
25	18
26	91
27	22
28	13
29	24
30	65
31	28
32	39
33	32
34	45
35	26
36	51
37	38
38	17
39	19
40	34
41	57
42	40
43	63
44	44
45	69
46	50
47	23
48	36
49	115
50	42
51	55
52	46
53	75
54	52
55	81
56	56
57	87
58	62
59	29
60	31
61	58
62	93
63	64
64	99
65	68
66	105
67	74

n	a(n)
1	1
2	2
3	3
4	4
5	9
6	8
7	15
8	14
9	5
10	7
11	10
12	21
13	16
14	27
15	20
16	33
17	25
18	11
19	30
20	77
21	6
22	35
23	12
24	49
25	18
26	91
27	22
28	13
29	24
30	65
31	28
32	39
33	32
34	45
35	26
36	51
37	38
38	17
39	19
40	34
41	57
42	40
43	63
44	44
45	69
46	50
47	23
48	36
49	115
50	42
51	55
52	46
53	75
54	52
55	81
56	56
57	87
58	62
59	29
60	31
61	58
62	93
63	64
64	99
65	68
66	105
67	74