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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 5 |
| 2 | 20 |
| 3 | 120 |
| 4 | 540 |
| 5 | 6480 |
| 6 | 48600 |
| 7 | 874800 |
| 8 | 9185400 |
| 9 | 79606800 |
| 10 | 2388204000 |
| 11 | 27066312000 |
| 12 | 527793084000 |
| 13 | 22167309528000 |
| 14 | 498764464380000 |
| 15 | 8312741073000000 |
| 16 | 155171166696000000 |
| 17 | 9310270001760000000 |
| 18 | 198619093370880000000 |
| 19 | 6852358721295360000000 |
| 20 | 493369827933265920000000 |
[1,5,20,120,540,6480,48600,874800,9185400, 79606800,2388204000,27066312000,527793084000, 22167309528000,498764464380000,8312741073000000, 155171166696000000,9310270001760000000, 198619093370880000000,6852358721295360000000, 493369827933265920000000] |