A027428 - cp's OEIS frontend

A027428 Number of distinct products ij with 1 <= i < j <= n. (Number of terms appearing more than once in a 1-to-n multiplication table.)

n	a(n)
1	0
2	1
3	3
4	6
5	10
6	13
7	19
8	24
9	31
10	36
11	46
12	51
13	63
14	70
15	78
16	87
17	103
18	111
19	129
20	139
21	150
22	161
23	183
24	192
25	210
26	223
27	239
28	252
29	280
30	291
31	321
32	337
33	354
34	371
35	390
36	403
37	439
38	458
39	478
40	493
41	533
42	549
43	591
44	611
45	631
46	654
47	700
48	717
49	752
50	774
51	800
52	823
53	875

[0, 1, 3, 6, 10, 13, 19, 24, 31, 36, 46, 51, 63, 70, 78, 87, 103, 111, 129, 139, 150, 161, 183, 192, 210, 223, 239, 252, 280, 291, 321, 337, 354, 371, 390, 403, 439, 458, 478, 493, 533, 549, 591, 611, 631, 654, 700, 717, 752, 774, 800, 823, 875]

cp's OEIS Frontend

A027428 Number of distinct products ij with 1 <= i < j <= n. (Number of terms appearing more than once in a 1-to-n multiplication table.)

Table of values

List of values

n	a(n)
1	0
2	1
3	3
4	6
5	10
6	13
7	19
8	24
9	31
10	36
11	46
12	51
13	63
14	70
15	78
16	87
17	103
18	111
19	129
20	139
21	150
22	161
23	183
24	192
25	210
26	223
27	239
28	252
29	280
30	291
31	321
32	337
33	354
34	371
35	390
36	403
37	439
38	458
39	478
40	493
41	533
42	549
43	591
44	611
45	631
46	654
47	700
48	717
49	752
50	774
51	800
52	823
53	875

n	a(n)
1	0
2	1
3	3
4	6
5	10
6	13
7	19
8	24
9	31
10	36
11	46
12	51
13	63
14	70
15	78
16	87
17	103
18	111
19	129
20	139
21	150
22	161
23	183
24	192
25	210
26	223
27	239
28	252
29	280
30	291
31	321
32	337
33	354
34	371
35	390
36	403
37	439
38	458
39	478
40	493
41	533
42	549
43	591
44	611
45	631
46	654
47	700
48	717
49	752
50	774
51	800
52	823
53	875

n	a(n)
1	0
2	1
3	3
4	6
5	10
6	13
7	19
8	24
9	31
10	36
11	46
12	51
13	63
14	70
15	78
16	87
17	103
18	111
19	129
20	139
21	150
22	161
23	183
24	192
25	210
26	223
27	239
28	252
29	280
30	291
31	321
32	337
33	354
34	371
35	390
36	403
37	439
38	458
39	478
40	493
41	533
42	549
43	591
44	611
45	631
46	654
47	700
48	717
49	752
50	774
51	800
52	823
53	875