A269254 - cp's OEIS frontend

A269254 To find a(n), define a sequence by s(k) = n*s(k-1) - s(k-2), with s(0) = 1, s(1) = n + 1; then a(n) is the smallest index k such that s(k) is prime, or -1 if no such k exists.

n	a(n)
1	1
2	1
3	2
4	1
5	2
6	1
7	-1
8	2
9	2
10	1
11	2
12	1
13	2
14	-1
15	2
16	1
17	3
18	1
19	2
20	2
21	2
22	1
23	-1
24	2
25	6
26	2
27	3
28	1
29	3
30	1
31	2
32	9
33	9
34	-1
35	2
36	1
37	6
38	2
39	2
40	1
41	2
42	1
43	5
44	2
45	2
46	1
47	-1
48	2
49	5
50	2
51	9
52	1
53	2
54	2
55	2
56	2
57	6
58	1
59	2
60	1
61	14
62	-1
63	5
64	2
65	2
66	1
67	5
68	2
69	3
70	1
71	6
72	1
73	8
74	3
75	6
76	2
77	3
78	1
79	-1
80	3
81	18
82	1
83	2
84	3
85	2
86	2
87	3
88	1
89	2
90	9
91	3
92	5
93	2
94	2
95	96
96	1
97	3
98	-1
99	5
100	1
101	2
102	1
103	2
104	15
105	14
106	1
107	44
108	1
109	3
110	-1

[1, 1, 2, 1, 2, 1, -1, 2, 2, 1, 2, 1, 2, -1, 2, 1, 3, 1, 2, 2, 2, 1, -1, 2, 6, 2, 3, 1, 3, 1, 2, 9, 9, -1, 2, 1, 6, 2, 2, 1, 2, 1, 5, 2, 2, 1, -1, 2, 5, 2, 9, 1, 2, 2, 2, 2, 6, 1, 2, 1, 14, -1, 5, 2, 2, 1, 5, 2, 3, 1, 6, 1, 8, 3, 6, 2, 3, 1, -1, 3, 18, 1, 2, 3, 2, 2, 3, 1, 2, 9, 3, 5, 2, 2, 96, 1, 3, -1, 5, 1, 2, 1, 2, 15, 14, 1, 44, 1, 3, -1]

cp's OEIS Frontend

A269254 To find a(n), define a sequence by s(k) = n*s(k-1) - s(k-2), with s(0) = 1, s(1) = n + 1; then a(n) is the smallest index k such that s(k) is prime, or -1 if no such k exists.

Table of values

List of values

n	a(n)
1	1
2	1
3	2
4	1
5	2
6	1
7	-1
8	2
9	2
10	1
11	2
12	1
13	2
14	-1
15	2
16	1
17	3
18	1
19	2
20	2
21	2
22	1
23	-1
24	2
25	6
26	2
27	3
28	1
29	3
30	1
31	2
32	9
33	9
34	-1
35	2
36	1
37	6
38	2
39	2
40	1
41	2
42	1
43	5
44	2
45	2
46	1
47	-1
48	2
49	5
50	2
51	9
52	1
53	2
54	2
55	2
56	2
57	6
58	1
59	2
60	1
61	14
62	-1
63	5
64	2
65	2
66	1
67	5
68	2
69	3
70	1
71	6
72	1
73	8
74	3
75	6
76	2
77	3
78	1
79	-1
80	3
81	18
82	1
83	2
84	3
85	2
86	2
87	3
88	1
89	2
90	9
91	3
92	5
93	2
94	2
95	96
96	1
97	3
98	-1
99	5
100	1
101	2
102	1
103	2
104	15
105	14
106	1
107	44
108	1
109	3
110	-1

n	a(n)
1	1
2	1
3	2
4	1
5	2
6	1
7	-1
8	2
9	2
10	1
11	2
12	1
13	2
14	-1
15	2
16	1
17	3
18	1
19	2
20	2
21	2
22	1
23	-1
24	2
25	6
26	2
27	3
28	1
29	3
30	1
31	2
32	9
33	9
34	-1
35	2
36	1
37	6
38	2
39	2
40	1
41	2
42	1
43	5
44	2
45	2
46	1
47	-1
48	2
49	5
50	2
51	9
52	1
53	2
54	2
55	2
56	2
57	6
58	1
59	2
60	1
61	14
62	-1
63	5
64	2
65	2
66	1
67	5
68	2
69	3
70	1
71	6
72	1
73	8
74	3
75	6
76	2
77	3
78	1
79	-1
80	3
81	18
82	1
83	2
84	3
85	2
86	2
87	3
88	1
89	2
90	9
91	3
92	5
93	2
94	2
95	96
96	1
97	3
98	-1
99	5
100	1
101	2
102	1
103	2
104	15
105	14
106	1
107	44
108	1
109	3
110	-1

n	a(n)
1	1
2	1
3	2
4	1
5	2
6	1
7	-1
8	2
9	2
10	1
11	2
12	1
13	2
14	-1
15	2
16	1
17	3
18	1
19	2
20	2
21	2
22	1
23	-1
24	2
25	6
26	2
27	3
28	1
29	3
30	1
31	2
32	9
33	9
34	-1
35	2
36	1
37	6
38	2
39	2
40	1
41	2
42	1
43	5
44	2
45	2
46	1
47	-1
48	2
49	5
50	2
51	9
52	1
53	2
54	2
55	2
56	2
57	6
58	1
59	2
60	1
61	14
62	-1
63	5
64	2
65	2
66	1
67	5
68	2
69	3
70	1
71	6
72	1
73	8
74	3
75	6
76	2
77	3
78	1
79	-1
80	3
81	18
82	1
83	2
84	3
85	2
86	2
87	3
88	1
89	2
90	9
91	3
92	5
93	2
94	2
95	96
96	1
97	3
98	-1
99	5
100	1
101	2
102	1
103	2
104	15
105	14
106	1
107	44
108	1
109	3
110	-1