A020053 - OEIS

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A020053 as a simple table

n	a(n)
0	1
1	0
2	1
3	2
4	9
5	46
6	260
7	1731
8	13220
9	114177
10	1100259
11	11702761
12	136177584
13	1720789475
14	23465311032
15	343446825119
16	5370259447316
17	89341588987179
18	1575660751228445
19	29364586727439203
20	576613703011533457

[1,0,1,2,9,46,260,1731,13220,114177,1100259, 11702761,136177584,1720789475,23465311032, 343446825119,5370259447316,89341588987179, 1575660751228445,29364586727439203, 576613703011533457]