A354718 - cp's OEIS frontend

A354718 a(n) is the smallest number b such that n, written in base 10 and interpreted as a base-b number, is a prime (or -1 if no such base exists).

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

[-1, 3, 4, -1, 6, -1, 8, -1, -1, 2, 2, 3, 4, 7, 6, 7, 10, 9, 10, -1, 3, -1, 4, -1, 6, -1, 8, -1, 10, -1, 4, 5, -1, 5, 6, -1, 8, 11, -1, -1, 7, -1, 5, -1, 6, -1, 9, -1, 11, -1, 6, 7, 8, 11, -1, 7, 8, 9, 10, -1, 7, -1, -1, -1, 7, -1, 9, -1, -1, -1, 10, 11, 8, 9]

cp's OEIS Frontend

A354718 a(n) is the smallest number b such that n, written in base 10 and interpreted as a base-b number, is a prime (or -1 if no such base exists).

Table of values

List of values

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

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

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