A012280 - OEIS

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A012280 as a simple table

n	a(n)
0	1
1	0
2	-1
3	-3
4	-6
5	30
6	270
7	1400
8	-3080
9	-86184
10	-893760
11	-754688
12	61595424
13	1201314400
14	5341239904
15	-68598744240
16	-2871938780672
17	-25391249097088
18	31527888993024
19	10819112145879168
20	155954430765392768

[1,0,-1,-3,-6,30,270,1400,-3080,-86184,-893760, -754688,61595424,1201314400,5341239904, -68598744240,-2871938780672,-25391249097088, 31527888993024,10819112145879168, 155954430765392768]