A007172 - OEIS

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A007172 as a simple table

n	a(n)
1	1
2	1
3	1
4	3
5	7
6	24
7	93
8	434
9	2110
10	10957
11	58713
12	321576
13	1792133
14	10131027
15	57949430
16	334970205
17	1953890318
18	11489753730
19	68054102361
20	405715557048

[1,1,1,3,7,24,93,434,2110,10957,58713,321576, 1792133,10131027,57949430,334970205,1953890318, 11489753730,68054102361,405715557048]