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| n | a(n) |
|---|---|
| 1 | 4 |
| 2 | 40 |
| 3 | 416 |
| 4 | 3808 |
| 5 | 33472 |
| 6 | 282752 |
| 7 | 2339072 |
| 8 | 19077632 |
| 9 | 154350592 |
| 10 | 1242703872 |
| 11 | 9977483264 |
| 12 | 79979520000 |
| 13 | 640542392320 |
| 14 | 5127428276224 |
| 15 | 41032860631040 |
| 16 | 328320884015104 |
| 17 | 2626816281149440 |
| 18 | 21015595535826944 |
| 19 | 168129300578435072 |
| 20 | 1345053647156805632 |
| 21 | 10760510547561545728 |
[4,40,416,3808,33472,282752,2339072,19077632, 154350592,1242703872,9977483264,79979520000, 640542392320,5127428276224,41032860631040, 328320884015104,2626816281149440, 21015595535826944,168129300578435072, 1345053647156805632,10760510547561545728] |