A025208 - OEIS

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A025208 as a simple table

n	a(n)
2	1
3	1
4	3
5	6
6	12
7	28
8	64
9	154
10	382
11	979
12	2583
13	6998
14	19421
15	55106
16	159595
17	471041
18	1414958
19	4320813
20	13399076
21	42157076
22	134459874
23	434427716
24	1420861672
25	4701420879

[1,1,3,6,12,28,64,154,382,979,2583,6998,19421, 55106,159595,471041,1414958,4320813,13399076, 42157076,134459874,434427716,1420861672, 4701420879]