A018996 - OEIS

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A018996 as a simple table

n	a(n)
2	3
3	9
4	52
5	291
6	1445
7	6420
8	32959
9	187727
10	1102665
11	6930612
12	46522650
13	320194002
14	2204132941
15	15091491681
16	102924219886

[3,9,52,291,1445,6420,32959,187727,1102665, 6930612,46522650,320194002,2204132941,15091491681, 102924219886]