A378500 - cp's OEIS frontend

A378500 a(1) = 2, then a(n) = a(n-1) - 2 for n even, a(n) = a(n-1) + 3 for n an odd prime or odd prime power, and a(n) = a(n-1) + 2 otherwise.

n	a(n)
1	2
2	0
3	3
4	1
5	4
6	2
7	5
8	3
9	6
10	4
11	7
12	5
13	8
14	6
15	8
16	6
17	9
18	7
19	10
20	8
21	10
22	8
23	11
24	9
25	12
26	10
27	13
28	11
29	14
30	12
31	15
32	13
33	15
34	13
35	15
36	13
37	16
38	14
39	16
40	14
41	17
42	15
43	18
44	16
45	18
46	16
47	19
48	17
49	20
50	18
51	20
52	18
53	21
54	19
55	21
56	19
57	21
58	19
59	22
60	20
61	23
62	21
63	23
64	21
65	23
66	21
67	24
68	22
69	24
70	22
71	25

[2, 0, 3, 1, 4, 2, 5, 3, 6, 4, 7, 5, 8, 6, 8, 6, 9, 7, 10, 8, 10, 8, 11, 9, 12, 10, 13, 11, 14, 12, 15, 13, 15, 13, 15, 13, 16, 14, 16, 14, 17, 15, 18, 16, 18, 16, 19, 17, 20, 18, 20, 18, 21, 19, 21, 19, 21, 19, 22, 20, 23, 21, 23, 21, 23, 21, 24, 22, 24, 22, 25]

cp's OEIS Frontend

A378500 a(1) = 2, then a(n) = a(n-1) - 2 for n even, a(n) = a(n-1) + 3 for n an odd prime or odd prime power, and a(n) = a(n-1) + 2 otherwise.

Table of values

List of values

n	a(n)
1	2
2	0
3	3
4	1
5	4
6	2
7	5
8	3
9	6
10	4
11	7
12	5
13	8
14	6
15	8
16	6
17	9
18	7
19	10
20	8
21	10
22	8
23	11
24	9
25	12
26	10
27	13
28	11
29	14
30	12
31	15
32	13
33	15
34	13
35	15
36	13
37	16
38	14
39	16
40	14
41	17
42	15
43	18
44	16
45	18
46	16
47	19
48	17
49	20
50	18
51	20
52	18
53	21
54	19
55	21
56	19
57	21
58	19
59	22
60	20
61	23
62	21
63	23
64	21
65	23
66	21
67	24
68	22
69	24
70	22
71	25

n	a(n)
1	2
2	0
3	3
4	1
5	4
6	2
7	5
8	3
9	6
10	4
11	7
12	5
13	8
14	6
15	8
16	6
17	9
18	7
19	10
20	8
21	10
22	8
23	11
24	9
25	12
26	10
27	13
28	11
29	14
30	12
31	15
32	13
33	15
34	13
35	15
36	13
37	16
38	14
39	16
40	14
41	17
42	15
43	18
44	16
45	18
46	16
47	19
48	17
49	20
50	18
51	20
52	18
53	21
54	19
55	21
56	19
57	21
58	19
59	22
60	20
61	23
62	21
63	23
64	21
65	23
66	21
67	24
68	22
69	24
70	22
71	25

n	a(n)
1	2
2	0
3	3
4	1
5	4
6	2
7	5
8	3
9	6
10	4
11	7
12	5
13	8
14	6
15	8
16	6
17	9
18	7
19	10
20	8
21	10
22	8
23	11
24	9
25	12
26	10
27	13
28	11
29	14
30	12
31	15
32	13
33	15
34	13
35	15
36	13
37	16
38	14
39	16
40	14
41	17
42	15
43	18
44	16
45	18
46	16
47	19
48	17
49	20
50	18
51	20
52	18
53	21
54	19
55	21
56	19
57	21
58	19
59	22
60	20
61	23
62	21
63	23
64	21
65	23
66	21
67	24
68	22
69	24
70	22
71	25