A370500 - cp's OEIS frontend

A370500 a(1) = 1, a(2) = 2; for n > 2, a(n) is the smallest unused positive number such that a(n) does not share a factor with a(n-1) but sopfr(a(n)) does share a factor with soprf(a(n-1)), where sopfr(k) is the sum of the primes dividing k, with repetition.

n	a(n)
1	1
2	2
3	9
4	4
5	15
6	8
7	3
8	14
9	27
10	20
11	77
12	16
13	21
14	5
15	6
16	25
17	18
18	35
19	24
20	65
21	32
22	33
23	7
24	10
25	49
26	12
27	115
28	36
29	55
30	39
31	50
32	51
33	26
34	81
35	38
36	105
37	44
38	91
39	30
40	119
41	57
42	11
43	28
44	45
45	62
46	85
47	42
48	95
49	64
50	69
51	13
52	22
53	63
54	74
55	75
56	56
57	169
58	60
59	121
60	40
61	123
62	70
63	87
64	98
65	93
66	17
67	52
68	99
69	145
70	66
71	133
72	72
73	125
74	46

[1, 2, 9, 4, 15, 8, 3, 14, 27, 20, 77, 16, 21, 5, 6, 25, 18, 35, 24, 65, 32, 33, 7, 10, 49, 12, 115, 36, 55, 39, 50, 51, 26, 81, 38, 105, 44, 91, 30, 119, 57, 11, 28, 45, 62, 85, 42, 95, 64, 69, 13, 22, 63, 74, 75, 56, 169, 60, 121, 40, 123, 70, 87, 98, 93, 17, 52, 99, 145, 66, 133, 72, 125, 46]

cp's OEIS Frontend

A370500 a(1) = 1, a(2) = 2; for n > 2, a(n) is the smallest unused positive number such that a(n) does not share a factor with a(n-1) but sopfr(a(n)) does share a factor with soprf(a(n-1)), where sopfr(k) is the sum of the primes dividing k, with repetition.

Table of values

List of values

n	a(n)
1	1
2	2
3	9
4	4
5	15
6	8
7	3
8	14
9	27
10	20
11	77
12	16
13	21
14	5
15	6
16	25
17	18
18	35
19	24
20	65
21	32
22	33
23	7
24	10
25	49
26	12
27	115
28	36
29	55
30	39
31	50
32	51
33	26
34	81
35	38
36	105
37	44
38	91
39	30
40	119
41	57
42	11
43	28
44	45
45	62
46	85
47	42
48	95
49	64
50	69
51	13
52	22
53	63
54	74
55	75
56	56
57	169
58	60
59	121
60	40
61	123
62	70
63	87
64	98
65	93
66	17
67	52
68	99
69	145
70	66
71	133
72	72
73	125
74	46

n	a(n)
1	1
2	2
3	9
4	4
5	15
6	8
7	3
8	14
9	27
10	20
11	77
12	16
13	21
14	5
15	6
16	25
17	18
18	35
19	24
20	65
21	32
22	33
23	7
24	10
25	49
26	12
27	115
28	36
29	55
30	39
31	50
32	51
33	26
34	81
35	38
36	105
37	44
38	91
39	30
40	119
41	57
42	11
43	28
44	45
45	62
46	85
47	42
48	95
49	64
50	69
51	13
52	22
53	63
54	74
55	75
56	56
57	169
58	60
59	121
60	40
61	123
62	70
63	87
64	98
65	93
66	17
67	52
68	99
69	145
70	66
71	133
72	72
73	125
74	46

n	a(n)
1	1
2	2
3	9
4	4
5	15
6	8
7	3
8	14
9	27
10	20
11	77
12	16
13	21
14	5
15	6
16	25
17	18
18	35
19	24
20	65
21	32
22	33
23	7
24	10
25	49
26	12
27	115
28	36
29	55
30	39
31	50
32	51
33	26
34	81
35	38
36	105
37	44
38	91
39	30
40	119
41	57
42	11
43	28
44	45
45	62
46	85
47	42
48	95
49	64
50	69
51	13
52	22
53	63
54	74
55	75
56	56
57	169
58	60
59	121
60	40
61	123
62	70
63	87
64	98
65	93
66	17
67	52
68	99
69	145
70	66
71	133
72	72
73	125
74	46