A012847 - OEIS

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A012847 as a simple table

n	a(n)
0	1
1	4
2	28
3	152
4	6928
5	2225408
6	348750400
7	38567316608
8	5024551512320
9	2238520490011648
10	1265695140964379648
11	555587429710072952832
12	218348017328527789264896
13	124784882666107086189330432

[1,4,28,152,6928,2225408,348750400,38567316608, 5024551512320,2238520490011648, 1265695140964379648,555587429710072952832, 218348017328527789264896, 124784882666107086189330432]