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| n | a(n) |
|---|---|
| 4 | 1 |
| 5 | 4 |
| 6 | 20 |
| 7 | 100 |
| 8 | 560 |
| 9 | 3416 |
| 10 | 22764 |
| 11 | 164640 |
| 12 | 1286175 |
| 13 | 10800460 |
| 14 | 97064396 |
| 15 | 929872944 |
| 16 | 9461716810 |
| 17 | 101926129200 |
| 18 | 1159018540400 |
| 19 | 13874662175520 |
| 20 | 174430929675615 |
| 21 | 2297878921894800 |
| 22 | 31655403616078550 |
| 23 | 455168137467988560 |
| 24 | 6819445400385661890 |
| 25 | 106288470495749772120 |
[1,4,20,100,560,3416,22764,164640,1286175, 10800460,97064396,929872944,9461716810, 101926129200,1159018540400,13874662175520, 174430929675615,2297878921894800, 31655403616078550,455168137467988560, 6819445400385661890,106288470495749772120] |