A003308 - OEIS

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A003308 as a simple table

n	a(n)
1	2
2	2
3	6
4	32
5	250
6	2592
7	33614
8	524288
9	9565938
10	200000000
11	4715895382
12	123834728448
13	3584320788074
14	113387824750592
15	3892390136718750
16	144115188075855872
17	5724846103019631586
18	242879062193188503552

[2,2,6,32,250,2592,33614,524288,9565938,200000000, 4715895382,123834728448,3584320788074, 113387824750592,3892390136718750, 144115188075855872,5724846103019631586, 242879062193188503552]