A018945 - OEIS

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A018945 as a simple table

n	a(n)
2	1
3	13
4	23
5	252
6	1011
7	7399
8	41917
9	288815
10	1888898
11	13146927
12	91142757
13	645483238
14	4591598912
15	32980554174
16	238209736716

[1,13,23,252,1011,7399,41917,288815,1888898, 13146927,91142757,645483238,4591598912, 32980554174,238209736716]