A103824 - cp's OEIS frontend

A103824 Choose a(n) to be the smallest number not yet used such that: a(1) = 1, a(2n) = prime, a(2n+1) = composite and partial sums are alternately composite or prime.

n	a(n)
1	1
2	3
3	9
4	2
5	4
6	5
7	35
8	7
9	65
10	11
11	15
12	13
13	21
14	17
15	25
16	19
17	55
18	23
19	49
20	29
21	91
22	31
23	27
24	37
25	115
26	41
27	77
28	43
29	121
30	47
31	85
32	53
33	125
34	59
35	39
36	61
37	33
38	67
39	133
40	71
41	143
42	73
43	119
44	79
45	95
46	83
47	81
48	89
49	145
50	97
51	51
52	101
53	99
54	103
55	45
56	107
57	57
58	109
59	87
60	113
61	69
62	127
63	75
64	131
65	111
66	137

[1, 3, 9, 2, 4, 5, 35, 7, 65, 11, 15, 13, 21, 17, 25, 19, 55, 23, 49, 29, 91, 31, 27, 37, 115, 41, 77, 43, 121, 47, 85, 53, 125, 59, 39, 61, 33, 67, 133, 71, 143, 73, 119, 79, 95, 83, 81, 89, 145, 97, 51, 101, 99, 103, 45, 107, 57, 109, 87, 113, 69, 127, 75, 131, 111, 137]

cp's OEIS Frontend

A103824 Choose a(n) to be the smallest number not yet used such that: a(1) = 1, a(2n) = prime, a(2n+1) = composite and partial sums are alternately composite or prime.

Table of values

List of values

n	a(n)
1	1
2	3
3	9
4	2
5	4
6	5
7	35
8	7
9	65
10	11
11	15
12	13
13	21
14	17
15	25
16	19
17	55
18	23
19	49
20	29
21	91
22	31
23	27
24	37
25	115
26	41
27	77
28	43
29	121
30	47
31	85
32	53
33	125
34	59
35	39
36	61
37	33
38	67
39	133
40	71
41	143
42	73
43	119
44	79
45	95
46	83
47	81
48	89
49	145
50	97
51	51
52	101
53	99
54	103
55	45
56	107
57	57
58	109
59	87
60	113
61	69
62	127
63	75
64	131
65	111
66	137

n	a(n)
1	1
2	3
3	9
4	2
5	4
6	5
7	35
8	7
9	65
10	11
11	15
12	13
13	21
14	17
15	25
16	19
17	55
18	23
19	49
20	29
21	91
22	31
23	27
24	37
25	115
26	41
27	77
28	43
29	121
30	47
31	85
32	53
33	125
34	59
35	39
36	61
37	33
38	67
39	133
40	71
41	143
42	73
43	119
44	79
45	95
46	83
47	81
48	89
49	145
50	97
51	51
52	101
53	99
54	103
55	45
56	107
57	57
58	109
59	87
60	113
61	69
62	127
63	75
64	131
65	111
66	137

n	a(n)
1	1
2	3
3	9
4	2
5	4
6	5
7	35
8	7
9	65
10	11
11	15
12	13
13	21
14	17
15	25
16	19
17	55
18	23
19	49
20	29
21	91
22	31
23	27
24	37
25	115
26	41
27	77
28	43
29	121
30	47
31	85
32	53
33	125
34	59
35	39
36	61
37	33
38	67
39	133
40	71
41	143
42	73
43	119
44	79
45	95
46	83
47	81
48	89
49	145
50	97
51	51
52	101
53	99
54	103
55	45
56	107
57	57
58	109
59	87
60	113
61	69
62	127
63	75
64	131
65	111
66	137