A143920 - OEIS

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A143920 as a simple table

n	a(n)
0	1
1	1
2	4
3	18
4	112
5	880
6	8256
7	90384
8	1131264
9	15927552
10	249164800
11	4287669760
12	80490393600
13	1636924403712
14	35850727342080
15	841260590499840
16	21056773882052608
17	559992309313503232
18	15768699458743959552

[1,1,4,18,112,880,8256,90384,1131264,15927552, 249164800,4287669760,80490393600,1636924403712, 35850727342080,841260590499840,21056773882052608, 559992309313503232,15768699458743959552]