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A221521 as a simple table

n a(n)
1 0
2 20
3 68
4 400
5 1940
6 9982
7 50400
8 256018
9 1297924
10 6584320
11 33394958
12 169387004
13 859152000
14 4357755890
15 22103183110
16 112110699524
17 568642349004
18 2884239836106
19 14629299498936
20 74202014273586
21 376363810775194

[0,20,68,400,1940,9982,50400,256018,1297924,
 6584320,33394958,169387004,859152000,4357755890,
 22103183110,112110699524,568642349004,
 2884239836106,14629299498936,74202014273586,
 376363810775194]

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Last modified October 28 12:28 EDT 2020. Contains 338054 sequences. (Running on oeis4.)