A379590 - cp's OEIS frontend

A379590 a(n) is the number of prime divisors d of n such that 2^d - 1 is prime.

n	a(n)
1	0
2	1
3	1
4	1
5	1
6	2
7	1
8	1
9	1
10	2
11	0
12	2
13	1
14	2
15	2
16	1
17	1
18	2
19	1
20	2
21	2
22	1
23	0
24	2
25	1
26	2
27	1
28	2
29	0
30	3
31	1
32	1
33	1
34	2
35	2
36	2
37	0
38	2
39	2
40	2
41	0
42	3
43	0
44	1
45	2
46	1
47	0
48	2
49	1
50	2
51	2
52	2
53	0
54	2
55	1
56	2
57	2
58	1
59	0
60	3
61	1
62	2
63	2
64	1
65	2
66	2
67	0
68	2
69	1
70	3
71	0
72	2
73	0
74	1
75	2
76	2
77	1
78	3
79	0
80	2
81	1
82	1
83	0
84	3
85	2
86	1
87	1
88	1
89	1
90	3
91	2
92	1
93	2
94	1
95	2
96	2
97	0
98	2
99	1
100	2

[0, 1, 1, 1, 1, 2, 1, 1, 1, 2, 0, 2, 1, 2, 2, 1, 1, 2, 1, 2, 2, 1, 0, 2, 1, 2, 1, 2, 0, 3, 1, 1, 1, 2, 2, 2, 0, 2, 2, 2, 0, 3, 0, 1, 2, 1, 0, 2, 1, 2, 2, 2, 0, 2, 1, 2, 2, 1, 0, 3, 1, 2, 2, 1, 2, 2, 0, 2, 1, 3, 0, 2, 0, 1, 2, 2, 1, 3, 0, 2, 1, 1, 0, 3, 2, 1, 1, 1, 1, 3, 2, 1, 2, 1, 2, 2, 0, 2, 1, 2]

cp's OEIS Frontend

A379590 a(n) is the number of prime divisors d of n such that 2^d - 1 is prime.

Table of values

List of values

n	a(n)
1	0
2	1
3	1
4	1
5	1
6	2
7	1
8	1
9	1
10	2
11	0
12	2
13	1
14	2
15	2
16	1
17	1
18	2
19	1
20	2
21	2
22	1
23	0
24	2
25	1
26	2
27	1
28	2
29	0
30	3
31	1
32	1
33	1
34	2
35	2
36	2
37	0
38	2
39	2
40	2
41	0
42	3
43	0
44	1
45	2
46	1
47	0
48	2
49	1
50	2
51	2
52	2
53	0
54	2
55	1
56	2
57	2
58	1
59	0
60	3
61	1
62	2
63	2
64	1
65	2
66	2
67	0
68	2
69	1
70	3
71	0
72	2
73	0
74	1
75	2
76	2
77	1
78	3
79	0
80	2
81	1
82	1
83	0
84	3
85	2
86	1
87	1
88	1
89	1
90	3
91	2
92	1
93	2
94	1
95	2
96	2
97	0
98	2
99	1
100	2

n	a(n)
1	0
2	1
3	1
4	1
5	1
6	2
7	1
8	1
9	1
10	2
11	0
12	2
13	1
14	2
15	2
16	1
17	1
18	2
19	1
20	2
21	2
22	1
23	0
24	2
25	1
26	2
27	1
28	2
29	0
30	3
31	1
32	1
33	1
34	2
35	2
36	2
37	0
38	2
39	2
40	2
41	0
42	3
43	0
44	1
45	2
46	1
47	0
48	2
49	1
50	2
51	2
52	2
53	0
54	2
55	1
56	2
57	2
58	1
59	0
60	3
61	1
62	2
63	2
64	1
65	2
66	2
67	0
68	2
69	1
70	3
71	0
72	2
73	0
74	1
75	2
76	2
77	1
78	3
79	0
80	2
81	1
82	1
83	0
84	3
85	2
86	1
87	1
88	1
89	1
90	3
91	2
92	1
93	2
94	1
95	2
96	2
97	0
98	2
99	1
100	2

n	a(n)
1	0
2	1
3	1
4	1
5	1
6	2
7	1
8	1
9	1
10	2
11	0
12	2
13	1
14	2
15	2
16	1
17	1
18	2
19	1
20	2
21	2
22	1
23	0
24	2
25	1
26	2
27	1
28	2
29	0
30	3
31	1
32	1
33	1
34	2
35	2
36	2
37	0
38	2
39	2
40	2
41	0
42	3
43	0
44	1
45	2
46	1
47	0
48	2
49	1
50	2
51	2
52	2
53	0
54	2
55	1
56	2
57	2
58	1
59	0
60	3
61	1
62	2
63	2
64	1
65	2
66	2
67	0
68	2
69	1
70	3
71	0
72	2
73	0
74	1
75	2
76	2
77	1
78	3
79	0
80	2
81	1
82	1
83	0
84	3
85	2
86	1
87	1
88	1
89	1
90	3
91	2
92	1
93	2
94	1
95	2
96	2
97	0
98	2
99	1
100	2