A075594 - cp's OEIS frontend

A075594 a(1) = 1, a(2n) = composite, a(2n+1) = prime and sum of two successive terms is alternately prime or composite.

n	a(n)
1	1
2	4
3	2
4	9
5	3
6	8
7	7
8	6
9	19
10	10
11	5
12	12
13	13
14	16
15	11
16	18
17	17
18	14
19	31
20	22
21	23
22	20
23	29
24	24
25	41
26	26
27	37
28	30
29	47
30	32
31	43
32	28
33	53
34	36
35	59
36	38
37	61
38	40
39	71
40	42
41	73
42	34
43	83
44	44
45	67
46	46
47	79
48	48
49	97
50	52
51	89
52	50
53	103
54	54
55	101
56	56
57	109
58	58
59	107
60	60
61	127
62	64
63	113
64	66
65	137
66	62
67	139
68	72
69	131

[1, 4, 2, 9, 3, 8, 7, 6, 19, 10, 5, 12, 13, 16, 11, 18, 17, 14, 31, 22, 23, 20, 29, 24, 41, 26, 37, 30, 47, 32, 43, 28, 53, 36, 59, 38, 61, 40, 71, 42, 73, 34, 83, 44, 67, 46, 79, 48, 97, 52, 89, 50, 103, 54, 101, 56, 109, 58, 107, 60, 127, 64, 113, 66, 137, 62, 139, 72, 131]

cp's OEIS Frontend

A075594 a(1) = 1, a(2n) = composite, a(2n+1) = prime and sum of two successive terms is alternately prime or composite.

Table of values

List of values

n	a(n)
1	1
2	4
3	2
4	9
5	3
6	8
7	7
8	6
9	19
10	10
11	5
12	12
13	13
14	16
15	11
16	18
17	17
18	14
19	31
20	22
21	23
22	20
23	29
24	24
25	41
26	26
27	37
28	30
29	47
30	32
31	43
32	28
33	53
34	36
35	59
36	38
37	61
38	40
39	71
40	42
41	73
42	34
43	83
44	44
45	67
46	46
47	79
48	48
49	97
50	52
51	89
52	50
53	103
54	54
55	101
56	56
57	109
58	58
59	107
60	60
61	127
62	64
63	113
64	66
65	137
66	62
67	139
68	72
69	131

n	a(n)
1	1
2	4
3	2
4	9
5	3
6	8
7	7
8	6
9	19
10	10
11	5
12	12
13	13
14	16
15	11
16	18
17	17
18	14
19	31
20	22
21	23
22	20
23	29
24	24
25	41
26	26
27	37
28	30
29	47
30	32
31	43
32	28
33	53
34	36
35	59
36	38
37	61
38	40
39	71
40	42
41	73
42	34
43	83
44	44
45	67
46	46
47	79
48	48
49	97
50	52
51	89
52	50
53	103
54	54
55	101
56	56
57	109
58	58
59	107
60	60
61	127
62	64
63	113
64	66
65	137
66	62
67	139
68	72
69	131

n	a(n)
1	1
2	4
3	2
4	9
5	3
6	8
7	7
8	6
9	19
10	10
11	5
12	12
13	13
14	16
15	11
16	18
17	17
18	14
19	31
20	22
21	23
22	20
23	29
24	24
25	41
26	26
27	37
28	30
29	47
30	32
31	43
32	28
33	53
34	36
35	59
36	38
37	61
38	40
39	71
40	42
41	73
42	34
43	83
44	44
45	67
46	46
47	79
48	48
49	97
50	52
51	89
52	50
53	103
54	54
55	101
56	56
57	109
58	58
59	107
60	60
61	127
62	64
63	113
64	66
65	137
66	62
67	139
68	72
69	131