A330310 - cp's OEIS frontend

A330310 Let p = prime(n); a(n) = (p-1)/2 if that is prime, or (p+1)/2 if that is prime, and otherwise p itself.

n	a(n)
1	2
2	2
3	2
4	3
5	5
6	7
7	17
8	19
9	11
10	29
11	31
12	19
13	41
14	43
15	23
16	53
17	29
18	31
19	67
20	71
21	37
22	79
23	41
24	89
25	97
26	101
27	103
28	53
29	109
30	113
31	127
32	131
33	137
34	139
35	149
36	151
37	79
38	163
39	83
40	173
41	89
42	181
43	191
44	97
45	197
46	199
47	211
48	223
49	113
50	229
51	233
52	239
53	241
54	251
55	257
56	131
57	269
58	271
59	139

[2, 2, 2, 3, 5, 7, 17, 19, 11, 29, 31, 19, 41, 43, 23, 53, 29, 31, 67, 71, 37, 79, 41, 89, 97, 101, 103, 53, 109, 113, 127, 131, 137, 139, 149, 151, 79, 163, 83, 173, 89, 181, 191, 97, 197, 199, 211, 223, 113, 229, 233, 239, 241, 251, 257, 131, 269, 271, 139]

cp's OEIS Frontend

A330310 Let p = prime(n); a(n) = (p-1)/2 if that is prime, or (p+1)/2 if that is prime, and otherwise p itself.

Table of values

List of values

n	a(n)
1	2
2	2
3	2
4	3
5	5
6	7
7	17
8	19
9	11
10	29
11	31
12	19
13	41
14	43
15	23
16	53
17	29
18	31
19	67
20	71
21	37
22	79
23	41
24	89
25	97
26	101
27	103
28	53
29	109
30	113
31	127
32	131
33	137
34	139
35	149
36	151
37	79
38	163
39	83
40	173
41	89
42	181
43	191
44	97
45	197
46	199
47	211
48	223
49	113
50	229
51	233
52	239
53	241
54	251
55	257
56	131
57	269
58	271
59	139

n	a(n)
1	2
2	2
3	2
4	3
5	5
6	7
7	17
8	19
9	11
10	29
11	31
12	19
13	41
14	43
15	23
16	53
17	29
18	31
19	67
20	71
21	37
22	79
23	41
24	89
25	97
26	101
27	103
28	53
29	109
30	113
31	127
32	131
33	137
34	139
35	149
36	151
37	79
38	163
39	83
40	173
41	89
42	181
43	191
44	97
45	197
46	199
47	211
48	223
49	113
50	229
51	233
52	239
53	241
54	251
55	257
56	131
57	269
58	271
59	139

n	a(n)
1	2
2	2
3	2
4	3
5	5
6	7
7	17
8	19
9	11
10	29
11	31
12	19
13	41
14	43
15	23
16	53
17	29
18	31
19	67
20	71
21	37
22	79
23	41
24	89
25	97
26	101
27	103
28	53
29	109
30	113
31	127
32	131
33	137
34	139
35	149
36	151
37	79
38	163
39	83
40	173
41	89
42	181
43	191
44	97
45	197
46	199
47	211
48	223
49	113
50	229
51	233
52	239
53	241
54	251
55	257
56	131
57	269
58	271
59	139