A257312 - cp's OEIS frontend

A257312 a(1) = 6; a(2) = 7; for n > 2, a(n) is the smallest number of the form prime + 4 not already used which shares a factor with a(n-1).

n	a(n)
1	6
2	7
3	21
4	9
5	15
6	27
7	33
8	11
9	77
10	35
11	45
12	51
13	17
14	153
15	57
16	63
17	75
18	65
19	105
20	87
21	93
22	111
23	117
24	135
25	141
26	47
27	423
28	171
29	177
30	183
31	195
32	143
33	231
34	161
35	23
36	437
37	285
38	155
39	185
40	215
41	245
42	203
43	261
44	201
45	237
46	243
47	255
48	267
49	273
50	287
51	41
52	861
53	297
54	275
55	315
56	321
57	107

[6, 7, 21, 9, 15, 27, 33, 11, 77, 35, 45, 51, 17, 153, 57, 63, 75, 65, 105, 87, 93, 111, 117, 135, 141, 47, 423, 171, 177, 183, 195, 143, 231, 161, 23, 437, 285, 155, 185, 215, 245, 203, 261, 201, 237, 243, 255, 267, 273, 287, 41, 861, 297, 275, 315, 321, 107]

cp's OEIS Frontend

A257312 a(1) = 6; a(2) = 7; for n > 2, a(n) is the smallest number of the form prime + 4 not already used which shares a factor with a(n-1).

Table of values

List of values

n	a(n)
1	6
2	7
3	21
4	9
5	15
6	27
7	33
8	11
9	77
10	35
11	45
12	51
13	17
14	153
15	57
16	63
17	75
18	65
19	105
20	87
21	93
22	111
23	117
24	135
25	141
26	47
27	423
28	171
29	177
30	183
31	195
32	143
33	231
34	161
35	23
36	437
37	285
38	155
39	185
40	215
41	245
42	203
43	261
44	201
45	237
46	243
47	255
48	267
49	273
50	287
51	41
52	861
53	297
54	275
55	315
56	321
57	107

n	a(n)
1	6
2	7
3	21
4	9
5	15
6	27
7	33
8	11
9	77
10	35
11	45
12	51
13	17
14	153
15	57
16	63
17	75
18	65
19	105
20	87
21	93
22	111
23	117
24	135
25	141
26	47
27	423
28	171
29	177
30	183
31	195
32	143
33	231
34	161
35	23
36	437
37	285
38	155
39	185
40	215
41	245
42	203
43	261
44	201
45	237
46	243
47	255
48	267
49	273
50	287
51	41
52	861
53	297
54	275
55	315
56	321
57	107

n	a(n)
1	6
2	7
3	21
4	9
5	15
6	27
7	33
8	11
9	77
10	35
11	45
12	51
13	17
14	153
15	57
16	63
17	75
18	65
19	105
20	87
21	93
22	111
23	117
24	135
25	141
26	47
27	423
28	171
29	177
30	183
31	195
32	143
33	231
34	161
35	23
36	437
37	285
38	155
39	185
40	215
41	245
42	203
43	261
44	201
45	237
46	243
47	255
48	267
49	273
50	287
51	41
52	861
53	297
54	275
55	315
56	321
57	107