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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 20 |
| 3 | 80 |
| 4 | 340 |
| 5 | 1360 |
| 6 | 5520 |
| 7 | 22080 |
| 8 | 88660 |
| 9 | 354640 |
| 10 | 1419920 |
| 11 | 5679680 |
| 12 | 22724240 |
| 13 | 90896960 |
| 14 | 363609920 |
| 15 | 1454439680 |
| 16 | 5817847380 |
| 17 | 23271389520 |
| 18 | 93085912720 |
| 19 | 372343650880 |
| 20 | 1489376023440 |
| 21 | 5957504093760 |
| 22 | 23830022054720 |
| 23 | 95320088218880 |
| 24 | 381280375599760 |
| 25 | 1525121502399040 |
[1,4,20,80,340,1360,5520,22080,88660,354640, 1419920,5679680,22724240,90896960,363609920, 1454439680,5817847380,23271389520,93085912720, 372343650880,1489376023440,5957504093760, 23830022054720,95320088218880,381280375599760, 1525121502399040] |