A268221 - cp's OEIS frontend

A268221 Triangle read by rows: T(n,k) (n>=4, k=3..n-1) is the number of topologies t on n points having exactly k open sets such that t contains exactly one open set of size m for each m in {0,3,4,5,...,s,n} where s is the size of the largest proper open set in t.

n	a(n)
4	4
5	10
6	20
7	20
8	60
9	120
10	35
11	140
12	420
13	840
14	56
15	280
16	1120
17	3360
18	6720
19	84
20	504
21	2520
22	10080
23	30240
24	60480
25	120
26	840
27	5040
28	25200
29	100800
30	302400
31	604800
32	165
33	1320
34	9240
35	55440
36	277200
37	1108800
38	3326400
39	6652800
40	220
41	1980
42	15840
43	110880
44	665280
45	3326400
46	13305600
47	39916800
48	79833600

[4, 10, 20, 20, 60, 120, 35, 140, 420, 840, 56, 280, 1120, 3360, 6720, 84, 504, 2520, 10080, 30240, 60480, 120, 840, 5040, 25200, 100800, 302400, 604800, 165, 1320, 9240, 55440, 277200, 1108800, 3326400, 6652800, 220, 1980, 15840, 110880, 665280, 3326400, 13305600, 39916800, 79833600]

cp's OEIS Frontend

A268221 Triangle read by rows: T(n,k) (n>=4, k=3..n-1) is the number of topologies t on n points having exactly k open sets such that t contains exactly one open set of size m for each m in {0,3,4,5,...,s,n} where s is the size of the largest proper open set in t.

Table of values

List of values