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A108680 as a simple table

n a(n)
0 1
1 18
2 140
3 700
4 2646
5 8232
6 22176
7 53460
8 117975
9 242242
10 468468
11 861224
12 1516060
13 2570400
14 4217088
15 6720984
16 10439037
17 15844290
18 23554300
19 34364484
20 49286930
21 69595240
22 96876000
23 133087500
24 180626355
25 242402706
26 321924708
27 423393040

[1,18,140,700,2646,8232,22176,53460,117975,242242,
 468468,861224,1516060,2570400,4217088,6720984,
 10439037,15844290,23554300,34364484,49286930,
 69595240,96876000,133087500,180626355,242402706,
 321924708,423393040]

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Last modified January 22 13:41 EST 2020. Contains 331149 sequences. (Running on oeis4.)