A308639 - cp's OEIS frontend

A308639 a(n) is the number of pairs (i,j) such that 0 < i < j < n-1 and the points (i, a(i)), (j, a(j)) and (n-1, a(n-1)) are aligned.

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

[0, 0, 0, 1, 0, 3, 1, 0, 6, 3, 1, 1, 3, 1, 6, 1, 10, 0, 11, 2, 2, 2, 2, 5, 0, 15, 1, 16, 0, 21, 1, 22, 2, 7, 1, 29, 2, 11, 0, 31, 2, 16, 1, 36, 9, 0, 38, 3, 5, 2, 21, 0, 45, 4, 3, 11, 3, 12, 1, 45, 0, 56, 0, 69, 1, 56, 3, 16, 4, 5, 3, 25, 1, 69, 1, 79, 0, 82, 1]

cp's OEIS Frontend

A308639 a(n) is the number of pairs (i,j) such that 0 < i < j < n-1 and the points (i, a(i)), (j, a(j)) and (n-1, a(n-1)) are aligned.

Table of values

List of values

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

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

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