A348257 - cp's OEIS frontend

A348257 Number of ways we can write [n] as the union of 2 sets of sizes i, j which intersect in exactly 2 elements (2 < i,j < n; i = j allowed).

n	a(n)
4	6
5	30
6	105
7	315
8	868
9	2268
10	5715
11	14025
12	33726
13	79794
14	186277
15	429975
16	982920
17	2228088
18	5013351
19	11206485
20	24903490
21	55050030
22	121110297
23	265289475
24	578813676
25	1258290900
26	2726297275
27	5888802465
28	12683574918
29	27246198378
30	58384711245
31	124822486575
32	266287971856
33	566935682544

[6, 30, 105, 315, 868, 2268, 5715, 14025, 33726, 79794, 186277, 429975, 982920, 2228088, 5013351, 11206485, 24903490, 55050030, 121110297, 265289475, 578813676, 1258290900, 2726297275, 5888802465, 12683574918, 27246198378, 58384711245, 124822486575, 266287971856, 566935682544]

cp's OEIS Frontend

A348257 Number of ways we can write [n] as the union of 2 sets of sizes i, j which intersect in exactly 2 elements (2 < i,j < n; i = j allowed).

Table of values

List of values