A184183 - cp's OEIS frontend

A184183 Triangle read by rows: T(n,k) is the number of permutations of {1,2,...,n} having k blocks of length 2 (0 <= k <= floor(n/2)). A block of a permutation is a maximal sequence of consecutive integers which appear in consecutive positions. For example, the permutation 5412367 has 4 blocks: 5, 4, 123, and 67; one of them is of length 2.

n	a(n)
0	1
1	1
2	1
3	1
4	4
5	2
6	14
7	9
8	1
9	65
10	46
11	9
12	366
13	285
14	66
15	3
16	2451
17	2006
18	539
19	44
20	18949
21	16054
22	4776
23	530
24	11
25	166033
26	144128
27	46230
28	6224
29	265
30	1624948
31	1436322
32	487573
33	75269
34	4635
35	53
36	17561350
37	15740718
38	5584332
39	954116
40	74430
41	1854
42	207650171
43	188194591
44	69157935
45	12776470
46	1177625
47	44499
48	309

[1, 1, 1, 1, 4, 2, 14, 9, 1, 65, 46, 9, 366, 285, 66, 3, 2451, 2006, 539, 44, 18949, 16054, 4776, 530, 11, 166033, 144128, 46230, 6224, 265, 1624948, 1436322, 487573, 75269, 4635, 53, 17561350, 15740718, 5584332, 954116, 74430, 1854, 207650171, 188194591, 69157935, 12776470, 1177625, 44499, 309]

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