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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 8 |
| 3 | 90 |
| 4 | 1408 |
| 5 | 28350 |
| 6 | 697344 |
| 7 | 20264244 |
| 8 | 679313408 |
| 9 | 25805186550 |
| 10 | 1095482736640 |
| 11 | 51397070440716 |
| 12 | 2640925289349120 |
| 13 | 147491783753286700 |
| 14 | 8895880971425939456 |
| 15 | 576279075821454657000 |
| 16 | 39905347440408027725824 |
| 17 | 2941534126495441574472870 |
| 18 | 229966392623413457628168192 |
[1,1,8,90,1408,28350,697344,20264244,679313408, 25805186550,1095482736640,51397070440716, 2640925289349120,147491783753286700, 8895880971425939456,576279075821454657000, 39905347440408027725824,2941534126495441574472870, 229966392623413457628168192] |