A222859 - OEIS

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A222859 as a simple table

n	a(n)
1	20
2	123
3	2460
4	22620
5	452400
6	5631696
7	123774620
8	1750579287
9	38886003660
10	616343677120
11	13645322944000
12	228861094261117
13	5026600983006000
14	87653141405083368
15	1904562716219017600
16	34122352692143937360

[20,123,2460,22620,452400,5631696,123774620, 1750579287,38886003660,616343677120, 13645322944000,228861094261117,5026600983006000, 87653141405083368,1904562716219017600, 34122352692143937360]