A064413 - cp's OEIS frontend

A064413 EKG sequence (or ECG sequence): a(1) = 1; a(2) = 2; for n > 2, a(n) = smallest number not already used which shares a factor with a(n-1).

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	30
24	25
25	35
26	28
27	26
28	13
29	39
30	36
31	32
32	34
33	17
34	51
35	42
36	38
37	19
38	57
39	45
40	40
41	44
42	46
43	23
44	69
45	48
46	50
47	52
48	54
49	56
50	49
51	63
52	60
53	55
54	65
55	70
56	58
57	29
58	87
59	66
60	62
61	31
62	93
63	72
64	64
65	68
66	74
67	37
68	111
69	75
70	78
71	76
72	80
73	82

[1, 2, 4, 6, 3, 9, 12, 8, 10, 5, 15, 18, 14, 7, 21, 24, 16, 20, 22, 11, 33, 27, 30, 25, 35, 28, 26, 13, 39, 36, 32, 34, 17, 51, 42, 38, 19, 57, 45, 40, 44, 46, 23, 69, 48, 50, 52, 54, 56, 49, 63, 60, 55, 65, 70, 58, 29, 87, 66, 62, 31, 93, 72, 64, 68, 74, 37, 111, 75, 78, 76, 80, 82]

cp's OEIS Frontend

A064413 EKG sequence (or ECG sequence): a(1) = 1; a(2) = 2; for n > 2, a(n) = smallest number not already used which shares a factor with a(n-1).

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	30
24	25
25	35
26	28
27	26
28	13
29	39
30	36
31	32
32	34
33	17
34	51
35	42
36	38
37	19
38	57
39	45
40	40
41	44
42	46
43	23
44	69
45	48
46	50
47	52
48	54
49	56
50	49
51	63
52	60
53	55
54	65
55	70
56	58
57	29
58	87
59	66
60	62
61	31
62	93
63	72
64	64
65	68
66	74
67	37
68	111
69	75
70	78
71	76
72	80
73	82

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	30
24	25
25	35
26	28
27	26
28	13
29	39
30	36
31	32
32	34
33	17
34	51
35	42
36	38
37	19
38	57
39	45
40	40
41	44
42	46
43	23
44	69
45	48
46	50
47	52
48	54
49	56
50	49
51	63
52	60
53	55
54	65
55	70
56	58
57	29
58	87
59	66
60	62
61	31
62	93
63	72
64	64
65	68
66	74
67	37
68	111
69	75
70	78
71	76
72	80
73	82

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	30
24	25
25	35
26	28
27	26
28	13
29	39
30	36
31	32
32	34
33	17
34	51
35	42
36	38
37	19
38	57
39	45
40	40
41	44
42	46
43	23
44	69
45	48
46	50
47	52
48	54
49	56
50	49
51	63
52	60
53	55
54	65
55	70
56	58
57	29
58	87
59	66
60	62
61	31
62	93
63	72
64	64
65	68
66	74
67	37
68	111
69	75
70	78
71	76
72	80
73	82