A241531 - cp's OEIS frontend

A241531 a(n) = smallest k>=1 such that 2*prime(n) - k^2 is semiprime (or 0 if there is no such k).

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

[0, 0, 1, 2, 1, 1, 1, 2, 5, 1, 2, 3, 5, 1, 1, 7, 5, 1, 1, 1, 1, 4, 5, 1, 3, 1, 1, 1, 1, 3, 1, 3, 3, 2, 3, 1, 3, 5, 5, 5, 7, 1, 1, 2, 1, 2, 3, 1, 1, 2, 7, 3, 1, 1, 3, 3, 1, 2, 1, 3, 1, 7, 5, 5, 2, 1, 6, 5, 3, 1, 3, 1, 4, 1, 3, 7, 5, 1, 3, 1, 5, 1, 7, 1, 3, 13]

cp's OEIS Frontend

A241531 a(n) = smallest k>=1 such that 2*prime(n) - k^2 is semiprime (or 0 if there is no such k).

Table of values

List of values

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

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

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