A081386 - cp's OEIS frontend

A081386 Number of unitary prime divisors of central binomial coefficient, C(2n,n) = A000984(n), i.e., number of those prime factors in C(2n,n), whose exponent equals one.

n	a(n)
1	1
2	2
3	1
4	3
5	1
6	3
7	3
8	4
9	4
10	4
11	5
12	5
13	4
14	3
15	5
16	7
17	6
18	7
19	7
20	8
21	9
22	9
23	6
24	7
25	7
26	7
27	8
28	11
29	12
30	11
31	11
32	11
33	12
34	12
35	12
36	13
37	13
38	13
39	11
40	13
41	12
42	14
43	13
44	13
45	15
46	14
47	14
48	14
49	15
50	16
51	16
52	16
53	17
54	19
55	18
56	17
57	18
58	19
59	18
60	19
61	18
62	18
63	18
64	20
65	18
66	21
67	22
68	20
69	20
70	20
71	20
72	20
73	20
74	19
75	21
76	21
77	24
78	23

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

cp's OEIS Frontend

A081386 Number of unitary prime divisors of central binomial coefficient, C(2n,n) = A000984(n), i.e., number of those prime factors in C(2n,n), whose exponent equals one.

Table of values

List of values

n	a(n)
1	1
2	2
3	1
4	3
5	1
6	3
7	3
8	4
9	4
10	4
11	5
12	5
13	4
14	3
15	5
16	7
17	6
18	7
19	7
20	8
21	9
22	9
23	6
24	7
25	7
26	7
27	8
28	11
29	12
30	11
31	11
32	11
33	12
34	12
35	12
36	13
37	13
38	13
39	11
40	13
41	12
42	14
43	13
44	13
45	15
46	14
47	14
48	14
49	15
50	16
51	16
52	16
53	17
54	19
55	18
56	17
57	18
58	19
59	18
60	19
61	18
62	18
63	18
64	20
65	18
66	21
67	22
68	20
69	20
70	20
71	20
72	20
73	20
74	19
75	21
76	21
77	24
78	23

n	a(n)
1	1
2	2
3	1
4	3
5	1
6	3
7	3
8	4
9	4
10	4
11	5
12	5
13	4
14	3
15	5
16	7
17	6
18	7
19	7
20	8
21	9
22	9
23	6
24	7
25	7
26	7
27	8
28	11
29	12
30	11
31	11
32	11
33	12
34	12
35	12
36	13
37	13
38	13
39	11
40	13
41	12
42	14
43	13
44	13
45	15
46	14
47	14
48	14
49	15
50	16
51	16
52	16
53	17
54	19
55	18
56	17
57	18
58	19
59	18
60	19
61	18
62	18
63	18
64	20
65	18
66	21
67	22
68	20
69	20
70	20
71	20
72	20
73	20
74	19
75	21
76	21
77	24
78	23

n	a(n)
1	1
2	2
3	1
4	3
5	1
6	3
7	3
8	4
9	4
10	4
11	5
12	5
13	4
14	3
15	5
16	7
17	6
18	7
19	7
20	8
21	9
22	9
23	6
24	7
25	7
26	7
27	8
28	11
29	12
30	11
31	11
32	11
33	12
34	12
35	12
36	13
37	13
38	13
39	11
40	13
41	12
42	14
43	13
44	13
45	15
46	14
47	14
48	14
49	15
50	16
51	16
52	16
53	17
54	19
55	18
56	17
57	18
58	19
59	18
60	19
61	18
62	18
63	18
64	20
65	18
66	21
67	22
68	20
69	20
70	20
71	20
72	20
73	20
74	19
75	21
76	21
77	24
78	23