A370501 - cp's OEIS frontend

A370501 a(1) = 1, a(2) = 2; for n > 2, a(n) is the smallest unused positive number such that a(n) shares a factor with a(n-1) but sopfr(a(n)) does not 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	6
4	3
5	12
6	4
7	10
8	5
9	15
10	20
11	16
12	14
13	7
14	21
15	24
16	18
17	22
18	8
19	28
20	26
21	13
22	39
23	27
24	30
25	34
26	17
27	51
28	45
29	9
30	48
31	32
32	38
33	19
34	57
35	63
36	33
37	11
38	44
39	40
40	25
41	75
42	35
43	56
44	36
45	52
46	42
47	46
48	23
49	69
50	54
51	50
52	58
53	29
54	87
55	90
56	55
57	80
58	60
59	76
60	62
61	31
62	93
63	96
64	64
65	82
66	41
67	123
68	99
69	66
70	68
71	85
72	105
73	49
74	112

[1, 2, 6, 3, 12, 4, 10, 5, 15, 20, 16, 14, 7, 21, 24, 18, 22, 8, 28, 26, 13, 39, 27, 30, 34, 17, 51, 45, 9, 48, 32, 38, 19, 57, 63, 33, 11, 44, 40, 25, 75, 35, 56, 36, 52, 42, 46, 23, 69, 54, 50, 58, 29, 87, 90, 55, 80, 60, 76, 62, 31, 93, 96, 64, 82, 41, 123, 99, 66, 68, 85, 105, 49, 112]

cp's OEIS Frontend

A370501 a(1) = 1, a(2) = 2; for n > 2, a(n) is the smallest unused positive number such that a(n) shares a factor with a(n-1) but sopfr(a(n)) does not 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	6
4	3
5	12
6	4
7	10
8	5
9	15
10	20
11	16
12	14
13	7
14	21
15	24
16	18
17	22
18	8
19	28
20	26
21	13
22	39
23	27
24	30
25	34
26	17
27	51
28	45
29	9
30	48
31	32
32	38
33	19
34	57
35	63
36	33
37	11
38	44
39	40
40	25
41	75
42	35
43	56
44	36
45	52
46	42
47	46
48	23
49	69
50	54
51	50
52	58
53	29
54	87
55	90
56	55
57	80
58	60
59	76
60	62
61	31
62	93
63	96
64	64
65	82
66	41
67	123
68	99
69	66
70	68
71	85
72	105
73	49
74	112

n	a(n)
1	1
2	2
3	6
4	3
5	12
6	4
7	10
8	5
9	15
10	20
11	16
12	14
13	7
14	21
15	24
16	18
17	22
18	8
19	28
20	26
21	13
22	39
23	27
24	30
25	34
26	17
27	51
28	45
29	9
30	48
31	32
32	38
33	19
34	57
35	63
36	33
37	11
38	44
39	40
40	25
41	75
42	35
43	56
44	36
45	52
46	42
47	46
48	23
49	69
50	54
51	50
52	58
53	29
54	87
55	90
56	55
57	80
58	60
59	76
60	62
61	31
62	93
63	96
64	64
65	82
66	41
67	123
68	99
69	66
70	68
71	85
72	105
73	49
74	112

n	a(n)
1	1
2	2
3	6
4	3
5	12
6	4
7	10
8	5
9	15
10	20
11	16
12	14
13	7
14	21
15	24
16	18
17	22
18	8
19	28
20	26
21	13
22	39
23	27
24	30
25	34
26	17
27	51
28	45
29	9
30	48
31	32
32	38
33	19
34	57
35	63
36	33
37	11
38	44
39	40
40	25
41	75
42	35
43	56
44	36
45	52
46	42
47	46
48	23
49	69
50	54
51	50
52	58
53	29
54	87
55	90
56	55
57	80
58	60
59	76
60	62
61	31
62	93
63	96
64	64
65	82
66	41
67	123
68	99
69	66
70	68
71	85
72	105
73	49
74	112