A012231 - OEIS

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A012231 as a simple table

n	a(n)
0	1
1	1
2	1
3	1
4	1
5	9
6	49
7	281
8	1345
9	13233
10	105441
11	1179729
12	10336833
13	144386553
14	1580651409
15	25501409961
16	316289380737
17	5869292202465
18	83559601907649
19	1744083324947745
20	27709107620492673
21	643531258862953065

[1,1,1,1,1,9,49,281,1345,13233,105441,1179729, 10336833,144386553,1580651409,25501409961, 316289380737,5869292202465,83559601907649, 1744083324947745,27709107620492673, 643531258862953065]