A103825 - cp's OEIS frontend

A103825 Choose a(n) to be the smallest number not yet used such that: a(1) = 1, a(2n) = composite, a(2n+1) = prime and partial sums are alternately prime or composite.

n	a(n)
1	1
2	4
3	3
4	9
5	5
6	15
7	2
8	8
9	7
10	25
11	11
12	49
13	13
14	21
15	17
16	33
17	19
18	27
19	23
20	39
21	29
22	119
23	31
24	77
25	37
26	35
27	41
28	51
29	43
30	45
31	47
32	55
33	53
34	57
35	59
36	91
37	61
38	65
39	67
40	87
41	71
42	69
43	73
44	93
45	79
46	85
47	83
48	95
49	89
50	63
51	97
52	81
53	101
54	99
55	103
56	75
57	107
58	105
59	109
60	141
61	113
62	115
63	127
64	125
65	131
66	111
67	137

[1, 4, 3, 9, 5, 15, 2, 8, 7, 25, 11, 49, 13, 21, 17, 33, 19, 27, 23, 39, 29, 119, 31, 77, 37, 35, 41, 51, 43, 45, 47, 55, 53, 57, 59, 91, 61, 65, 67, 87, 71, 69, 73, 93, 79, 85, 83, 95, 89, 63, 97, 81, 101, 99, 103, 75, 107, 105, 109, 141, 113, 115, 127, 125, 131, 111, 137]

cp's OEIS Frontend

A103825 Choose a(n) to be the smallest number not yet used such that: a(1) = 1, a(2n) = composite, a(2n+1) = prime and partial sums are alternately prime or composite.

Table of values

List of values

n	a(n)
1	1
2	4
3	3
4	9
5	5
6	15
7	2
8	8
9	7
10	25
11	11
12	49
13	13
14	21
15	17
16	33
17	19
18	27
19	23
20	39
21	29
22	119
23	31
24	77
25	37
26	35
27	41
28	51
29	43
30	45
31	47
32	55
33	53
34	57
35	59
36	91
37	61
38	65
39	67
40	87
41	71
42	69
43	73
44	93
45	79
46	85
47	83
48	95
49	89
50	63
51	97
52	81
53	101
54	99
55	103
56	75
57	107
58	105
59	109
60	141
61	113
62	115
63	127
64	125
65	131
66	111
67	137

n	a(n)
1	1
2	4
3	3
4	9
5	5
6	15
7	2
8	8
9	7
10	25
11	11
12	49
13	13
14	21
15	17
16	33
17	19
18	27
19	23
20	39
21	29
22	119
23	31
24	77
25	37
26	35
27	41
28	51
29	43
30	45
31	47
32	55
33	53
34	57
35	59
36	91
37	61
38	65
39	67
40	87
41	71
42	69
43	73
44	93
45	79
46	85
47	83
48	95
49	89
50	63
51	97
52	81
53	101
54	99
55	103
56	75
57	107
58	105
59	109
60	141
61	113
62	115
63	127
64	125
65	131
66	111
67	137

n	a(n)
1	1
2	4
3	3
4	9
5	5
6	15
7	2
8	8
9	7
10	25
11	11
12	49
13	13
14	21
15	17
16	33
17	19
18	27
19	23
20	39
21	29
22	119
23	31
24	77
25	37
26	35
27	41
28	51
29	43
30	45
31	47
32	55
33	53
34	57
35	59
36	91
37	61
38	65
39	67
40	87
41	71
42	69
43	73
44	93
45	79
46	85
47	83
48	95
49	89
50	63
51	97
52	81
53	101
54	99
55	103
56	75
57	107
58	105
59	109
60	141
61	113
62	115
63	127
64	125
65	131
66	111
67	137