A012878 - OEIS

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A012878 as a simple table

n	a(n)
0	1
1	1
2	1
3	-1
4	-7
5	5
6	145
7	499
8	-2063
9	-12055
10	128705
11	2156871
12	5154217
13	-24423763
14	510686033
15	27205910523
16	254809389793
17	2396435716433
18	27371394484993
19	1214149548475407
20	18728499608356185
21	375616253471952085

[1,1,1,-1,-7,5,145,499,-2063,-12055,128705, 2156871,5154217,-24423763,510686033,27205910523, 254809389793,2396435716433,27371394484993, 1214149548475407,18728499608356185, 375616253471952085]