A254537 - OEIS

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A254537 as a simple table

n	a(n)
1	4
2	20
3	105
4	576
5	3383
6	20393
7	121774
8	709169
9	4121638
10	24622476
11	150895459
12	928855881
13	5659650136
14	34105862488
15	205228295685
16	1249619101830
17	7761595614134
18	48955797807546
19	308737202532449
20	1916725035118260

[4,20,105,576,3383,20393,121774,709169,4121638, 24622476,150895459,928855881,5659650136, 34105862488,205228295685,1249619101830, 7761595614134,48955797807546,308737202532449, 1916725035118260]