A047165 - cp's OEIS frontend

A047165 Number of nonempty subsets of {1,2,...,n} in which exactly 1/5 of the elements are <= n/2.

n	a(n)
1	0
2	0
3	0
4	0
5	0
6	0
7	3
8	4
9	20
10	25
11	75
12	90
13	210
14	245
15	511
16	588
17	1260
18	1458
19	3510
20	4125
21	10725
22	12705
23	32835
24	38830
25	96382
26	113399
27	273273
28	320411
29	770315
30	903175
31	2208115
32	2594540
33	6451500
34	7594920
35	18990768
36	22366458
37	55715562
38	65579982
39	162488703
40	191126529

[0, 0, 0, 0, 0, 0, 3, 4, 20, 25, 75, 90, 210, 245, 511, 588, 1260, 1458, 3510, 4125, 10725, 12705, 32835, 38830, 96382, 113399, 273273, 320411, 770315, 903175, 2208115, 2594540, 6451500, 7594920, 18990768, 22366458, 55715562, 65579982, 162488703, 191126529]

cp's OEIS Frontend

A047165 Number of nonempty subsets of {1,2,...,n} in which exactly 1/5 of the elements are <= n/2.

Table of values

List of values