A161680 - cp's OEIS frontend

A161680 a(n) = binomial(n,2): number of size-2 subsets of {0,1,...,n} that contain no consecutive integers.

n	a(n)
0	0
1	0
2	1
3	3
4	6
5	10
6	15
7	21
8	28
9	36
10	45
11	55
12	66
13	78
14	91
15	105
16	120
17	136
18	153
19	171
20	190
21	210
22	231
23	253
24	276
25	300
26	325
27	351
28	378
29	406
30	435
31	465
32	496
33	528
34	561
35	595
36	630
37	666
38	703
39	741
40	780
41	820
42	861
43	903
44	946
45	990
46	1035
47	1081
48	1128
49	1176
50	1225
51	1275
52	1326
53	1378

[0, 0, 1, 3, 6, 10, 15, 21, 28, 36, 45, 55, 66, 78, 91, 105, 120, 136, 153, 171, 190, 210, 231, 253, 276, 300, 325, 351, 378, 406, 435, 465, 496, 528, 561, 595, 630, 666, 703, 741, 780, 820, 861, 903, 946, 990, 1035, 1081, 1128, 1176, 1225, 1275, 1326, 1378]

cp's OEIS Frontend

A161680 a(n) = binomial(n,2): number of size-2 subsets of {0,1,...,n} that contain no consecutive integers.

Table of values

List of values