A320848 - cp's OEIS frontend

A320848 Number of 2-element subsets of [n] whose sum is a triangular number.

n	a(n)
2	1
3	1
4	2
5	3
6	4
7	5
8	7
9	9
10	10
11	12
12	14
13	16
14	18
15	20
16	22
17	24
18	26
19	29
20	32
21	34
22	36
23	39
24	42
25	45
26	48
27	51
28	54
29	57
30	60
31	63
32	66
33	69
34	73
35	77
36	80
37	83
38	86
39	89
40	93
41	97
42	101
43	105
44	109
45	112
46	116
47	120
48	124
49	128
50	132
51	136
52	140
53	145
54	150
55	154
56	158
57	162
58	166
59	170
60	174
61	179
62	184
63	189

[1, 1, 2, 3, 4, 5, 7, 9, 10, 12, 14, 16, 18, 20, 22, 24, 26, 29, 32, 34, 36, 39, 42, 45, 48, 51, 54, 57, 60, 63, 66, 69, 73, 77, 80, 83, 86, 89, 93, 97, 101, 105, 109, 112, 116, 120, 124, 128, 132, 136, 140, 145, 150, 154, 158, 162, 166, 170, 174, 179, 184, 189]

cp's OEIS Frontend

A320848 Number of 2-element subsets of [n] whose sum is a triangular number.

Table of values

List of values

n	a(n)
2	1
3	1
4	2
5	3
6	4
7	5
8	7
9	9
10	10
11	12
12	14
13	16
14	18
15	20
16	22
17	24
18	26
19	29
20	32
21	34
22	36
23	39
24	42
25	45
26	48
27	51
28	54
29	57
30	60
31	63
32	66
33	69
34	73
35	77
36	80
37	83
38	86
39	89
40	93
41	97
42	101
43	105
44	109
45	112
46	116
47	120
48	124
49	128
50	132
51	136
52	140
53	145
54	150
55	154
56	158
57	162
58	166
59	170
60	174
61	179
62	184
63	189

n	a(n)
2	1
3	1
4	2
5	3
6	4
7	5
8	7
9	9
10	10
11	12
12	14
13	16
14	18
15	20
16	22
17	24
18	26
19	29
20	32
21	34
22	36
23	39
24	42
25	45
26	48
27	51
28	54
29	57
30	60
31	63
32	66
33	69
34	73
35	77
36	80
37	83
38	86
39	89
40	93
41	97
42	101
43	105
44	109
45	112
46	116
47	120
48	124
49	128
50	132
51	136
52	140
53	145
54	150
55	154
56	158
57	162
58	166
59	170
60	174
61	179
62	184
63	189

n	a(n)
2	1
3	1
4	2
5	3
6	4
7	5
8	7
9	9
10	10
11	12
12	14
13	16
14	18
15	20
16	22
17	24
18	26
19	29
20	32
21	34
22	36
23	39
24	42
25	45
26	48
27	51
28	54
29	57
30	60
31	63
32	66
33	69
34	73
35	77
36	80
37	83
38	86
39	89
40	93
41	97
42	101
43	105
44	109
45	112
46	116
47	120
48	124
49	128
50	132
51	136
52	140
53	145
54	150
55	154
56	158
57	162
58	166
59	170
60	174
61	179
62	184
63	189