A225721 - cp's OEIS frontend

A225721 Starting with x = n, the number of iterations of x := 2x - 1 until x is prime, or -1 if no prime exists.

n	a(n)
1	-1
2	0
3	0
4	1
5	0
6	1
7	0
8	2
9	1
10	1
11	0
12	1
13	0
14	2
15	1
16	1
17	0
18	3
19	0
20	6
21	1
22	1
23	0
24	1
25	2
26	2
27	1
28	2
29	0
30	1
31	0
32	8
33	3
34	1
35	2
36	1
37	0
38	2
39	5
40	1
41	0
42	1
43	0
44	2
45	1
46	2
47	0
48	583
49	1
50	2
51	1
52	1
53	0
54	1
55	1
56	4
57	1
58	2
59	0
60	5
61	0
62	4
63	7
64	1
65	2
66	1
67	0
68	2
69	1
70	1
71	0
72	3
73	0
74	2
75	1
76	1
77	4
78	3
79	0
80	2
81	3
82	1
83	0
84	1
85	2
86	4

[-1, 0, 0, 1, 0, 1, 0, 2, 1, 1, 0, 1, 0, 2, 1, 1, 0, 3, 0, 6, 1, 1, 0, 1, 2, 2, 1, 2, 0, 1, 0, 8, 3, 1, 2, 1, 0, 2, 5, 1, 0, 1, 0, 2, 1, 2, 0, 583, 1, 2, 1, 1, 0, 1, 1, 4, 1, 2, 0, 5, 0, 4, 7, 1, 2, 1, 0, 2, 1, 1, 0, 3, 0, 2, 1, 1, 4, 3, 0, 2, 3, 1, 0, 1, 2, 4]

cp's OEIS Frontend

A225721 Starting with x = n, the number of iterations of x := 2x - 1 until x is prime, or -1 if no prime exists.

Table of values

List of values

n	a(n)
1	-1
2	0
3	0
4	1
5	0
6	1
7	0
8	2
9	1
10	1
11	0
12	1
13	0
14	2
15	1
16	1
17	0
18	3
19	0
20	6
21	1
22	1
23	0
24	1
25	2
26	2
27	1
28	2
29	0
30	1
31	0
32	8
33	3
34	1
35	2
36	1
37	0
38	2
39	5
40	1
41	0
42	1
43	0
44	2
45	1
46	2
47	0
48	583
49	1
50	2
51	1
52	1
53	0
54	1
55	1
56	4
57	1
58	2
59	0
60	5
61	0
62	4
63	7
64	1
65	2
66	1
67	0
68	2
69	1
70	1
71	0
72	3
73	0
74	2
75	1
76	1
77	4
78	3
79	0
80	2
81	3
82	1
83	0
84	1
85	2
86	4

n	a(n)
1	-1
2	0
3	0
4	1
5	0
6	1
7	0
8	2
9	1
10	1
11	0
12	1
13	0
14	2
15	1
16	1
17	0
18	3
19	0
20	6
21	1
22	1
23	0
24	1
25	2
26	2
27	1
28	2
29	0
30	1
31	0
32	8
33	3
34	1
35	2
36	1
37	0
38	2
39	5
40	1
41	0
42	1
43	0
44	2
45	1
46	2
47	0
48	583
49	1
50	2
51	1
52	1
53	0
54	1
55	1
56	4
57	1
58	2
59	0
60	5
61	0
62	4
63	7
64	1
65	2
66	1
67	0
68	2
69	1
70	1
71	0
72	3
73	0
74	2
75	1
76	1
77	4
78	3
79	0
80	2
81	3
82	1
83	0
84	1
85	2
86	4

n	a(n)
1	-1
2	0
3	0
4	1
5	0
6	1
7	0
8	2
9	1
10	1
11	0
12	1
13	0
14	2
15	1
16	1
17	0
18	3
19	0
20	6
21	1
22	1
23	0
24	1
25	2
26	2
27	1
28	2
29	0
30	1
31	0
32	8
33	3
34	1
35	2
36	1
37	0
38	2
39	5
40	1
41	0
42	1
43	0
44	2
45	1
46	2
47	0
48	583
49	1
50	2
51	1
52	1
53	0
54	1
55	1
56	4
57	1
58	2
59	0
60	5
61	0
62	4
63	7
64	1
65	2
66	1
67	0
68	2
69	1
70	1
71	0
72	3
73	0
74	2
75	1
76	1
77	4
78	3
79	0
80	2
81	3
82	1
83	0
84	1
85	2
86	4