A270939 - OEIS

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A270939 as a simple table

n	a(n)
0	1
1	5
2	20
3	60
4	260
5	1148
6	4908
7	19800
8	79804
9	324408
10	1301600
11	5225644
12	20917704
13	83744756
14	335197576
15	1340967308

[1,5,20,60,260,1148,4908,19800,79804,324408, 1301600,5225644,20917704,83744756,335197576, 1340967308]