A178663 - cp's OEIS frontend

A178663 a(1)=1. For n>1, a(n) is the smallest number greater than a(n-1) such that exactly one of n and a(n) is prime and the other is composite.

n	a(n)
1	1
2	4
3	6
4	7
5	8
6	11
7	12
8	13
9	17
10	19
11	20
12	23
13	24
14	29
15	31
16	37
17	38
18	41
19	42
20	43
21	47
22	53
23	54
24	59
25	61
26	67
27	71
28	73
29	74
30	79
31	80
32	83
33	89
34	97
35	101
36	103
37	104
38	107
39	109
40	113
41	114
42	127
43	128
44	131
45	137
46	139
47	140
48	149
49	151
50	157
51	163
52	167
53	168
54	173
55	179
56	181
57	191
58	193
59	194
60	197
61	198
62	199

[1, 4, 6, 7, 8, 11, 12, 13, 17, 19, 20, 23, 24, 29, 31, 37, 38, 41, 42, 43, 47, 53, 54, 59, 61, 67, 71, 73, 74, 79, 80, 83, 89, 97, 101, 103, 104, 107, 109, 113, 114, 127, 128, 131, 137, 139, 140, 149, 151, 157, 163, 167, 168, 173, 179, 181, 191, 193, 194, 197, 198, 199]

cp's OEIS Frontend

A178663 a(1)=1. For n>1, a(n) is the smallest number greater than a(n-1) such that exactly one of n and a(n) is prime and the other is composite.

Table of values

List of values

n	a(n)
1	1
2	4
3	6
4	7
5	8
6	11
7	12
8	13
9	17
10	19
11	20
12	23
13	24
14	29
15	31
16	37
17	38
18	41
19	42
20	43
21	47
22	53
23	54
24	59
25	61
26	67
27	71
28	73
29	74
30	79
31	80
32	83
33	89
34	97
35	101
36	103
37	104
38	107
39	109
40	113
41	114
42	127
43	128
44	131
45	137
46	139
47	140
48	149
49	151
50	157
51	163
52	167
53	168
54	173
55	179
56	181
57	191
58	193
59	194
60	197
61	198
62	199

n	a(n)
1	1
2	4
3	6
4	7
5	8
6	11
7	12
8	13
9	17
10	19
11	20
12	23
13	24
14	29
15	31
16	37
17	38
18	41
19	42
20	43
21	47
22	53
23	54
24	59
25	61
26	67
27	71
28	73
29	74
30	79
31	80
32	83
33	89
34	97
35	101
36	103
37	104
38	107
39	109
40	113
41	114
42	127
43	128
44	131
45	137
46	139
47	140
48	149
49	151
50	157
51	163
52	167
53	168
54	173
55	179
56	181
57	191
58	193
59	194
60	197
61	198
62	199

n	a(n)
1	1
2	4
3	6
4	7
5	8
6	11
7	12
8	13
9	17
10	19
11	20
12	23
13	24
14	29
15	31
16	37
17	38
18	41
19	42
20	43
21	47
22	53
23	54
24	59
25	61
26	67
27	71
28	73
29	74
30	79
31	80
32	83
33	89
34	97
35	101
36	103
37	104
38	107
39	109
40	113
41	114
42	127
43	128
44	131
45	137
46	139
47	140
48	149
49	151
50	157
51	163
52	167
53	168
54	173
55	179
56	181
57	191
58	193
59	194
60	197
61	198
62	199