A243521 - OEIS

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A243521 as a simple table

n	a(n)
0	1
1	3
2	12
3	57
4	300
5	1701
6	10206
7	63825
8	411096
9	2702349
10	17992506
11	120543561
12	808224372
13	5400815829
14	35868103734
15	236354531841
16	1544182760496
17	10001335837725
18	64233753928722
19	409298268016761
20	2589206145139596

[1,3,12,57,300,1701,10206,63825,411096,2702349, 17992506,120543561,808224372,5400815829, 35868103734,236354531841,1544182760496, 10001335837725,64233753928722,409298268016761, 2589206145139596]