A250028 - cp's OEIS frontend

A250028 a(n) is the number of positive integers k <= n such that lpf(k^2 + 1) = lpf(n^2 + 1), where lpf() is the least prime factor function.

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

[1, 1, 2, 1, 3, 1, 4, 2, 5, 1, 6, 3, 7, 1, 8, 1, 9, 4, 10, 1, 11, 5, 12, 1, 13, 1, 14, 6, 15, 2, 16, 7, 17, 1, 18, 1, 19, 8, 20, 1, 21, 9, 22, 2, 23, 1, 24, 10, 25, 1, 26, 11, 27, 1, 28, 1, 29, 12, 30, 3, 31, 13, 32, 3, 33, 1, 34, 14, 35, 4, 36, 15, 37, 1, 38, 1]

cp's OEIS Frontend

A250028 a(n) is the number of positive integers k <= n such that lpf(k^2 + 1) = lpf(n^2 + 1), where lpf() is the least prime factor function.

Table of values

List of values

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

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

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