A257311 - cp's OEIS frontend

A257311 a(1) = 4; a(2) = 5; for n > 2, a(n) is the smallest number of the form prime + 2 not already used which shares a factor with a(n-1).

n	a(n)
1	4
2	5
3	15
4	9
5	21
6	7
7	49
8	63
9	33
10	39
11	13
12	91
13	105
14	25
15	45
16	55
17	75
18	69
19	81
20	99
21	111
22	129
23	43
24	559
25	169
26	195
27	85
28	115
29	165
30	141
31	153
32	159
33	183
34	61
35	549
36	201
37	213
38	225
39	175
40	133
41	19
42	285
43	231
44	243
45	273
46	259
47	315
48	235
49	265
50	295
51	355
52	375
53	279
54	31
55	403
56	351
57	309
58	103

[4, 5, 15, 9, 21, 7, 49, 63, 33, 39, 13, 91, 105, 25, 45, 55, 75, 69, 81, 99, 111, 129, 43, 559, 169, 195, 85, 115, 165, 141, 153, 159, 183, 61, 549, 201, 213, 225, 175, 133, 19, 285, 231, 243, 273, 259, 315, 235, 265, 295, 355, 375, 279, 31, 403, 351, 309, 103]

cp's OEIS Frontend

A257311 a(1) = 4; a(2) = 5; for n > 2, a(n) is the smallest number of the form prime + 2 not already used which shares a factor with a(n-1).

Table of values

List of values

n	a(n)
1	4
2	5
3	15
4	9
5	21
6	7
7	49
8	63
9	33
10	39
11	13
12	91
13	105
14	25
15	45
16	55
17	75
18	69
19	81
20	99
21	111
22	129
23	43
24	559
25	169
26	195
27	85
28	115
29	165
30	141
31	153
32	159
33	183
34	61
35	549
36	201
37	213
38	225
39	175
40	133
41	19
42	285
43	231
44	243
45	273
46	259
47	315
48	235
49	265
50	295
51	355
52	375
53	279
54	31
55	403
56	351
57	309
58	103

n	a(n)
1	4
2	5
3	15
4	9
5	21
6	7
7	49
8	63
9	33
10	39
11	13
12	91
13	105
14	25
15	45
16	55
17	75
18	69
19	81
20	99
21	111
22	129
23	43
24	559
25	169
26	195
27	85
28	115
29	165
30	141
31	153
32	159
33	183
34	61
35	549
36	201
37	213
38	225
39	175
40	133
41	19
42	285
43	231
44	243
45	273
46	259
47	315
48	235
49	265
50	295
51	355
52	375
53	279
54	31
55	403
56	351
57	309
58	103

n	a(n)
1	4
2	5
3	15
4	9
5	21
6	7
7	49
8	63
9	33
10	39
11	13
12	91
13	105
14	25
15	45
16	55
17	75
18	69
19	81
20	99
21	111
22	129
23	43
24	559
25	169
26	195
27	85
28	115
29	165
30	141
31	153
32	159
33	183
34	61
35	549
36	201
37	213
38	225
39	175
40	133
41	19
42	285
43	231
44	243
45	273
46	259
47	315
48	235
49	265
50	295
51	355
52	375
53	279
54	31
55	403
56	351
57	309
58	103