A056339 - OEIS

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A056339 as a simple table

n	a(n)
1	0
2	0
3	0
4	0
5	1
6	9
7	76
8	542
9	3523
10	21392
11	123680
12	690541
13	3756151
14	20042513
15	105394295
16	548123440
17	2826435403
18	14479201301
19	73794961960
20	374603863517
21	1895632969275
22	9568915248589
23	48208452866816

[0,0,0,0,1,9,76,542,3523,21392,123680,690541, 3756151,20042513,105394295,548123440,2826435403, 14479201301,73794961960,374603863517, 1895632969275,9568915248589,48208452866816]