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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 9 |
| 4 | 56 |
| 5 | 480 |
| 6 | 5094 |
| 7 | 65534 |
| 8 | 984808 |
| 9 | 16629264 |
| 10 | 312523680 |
| 11 | 6425601072 |
| 12 | 143775827832 |
| 13 | 3471659156784 |
| 14 | 90060216241800 |
| 15 | 2496918043296840 |
| 16 | 73703868906725184 |
| 17 | 2307477802376274048 |
| 18 | 76376765284713220032 |
| 19 | 2664806795257276548288 |
| 20 | 97747916619062963335680 |
[1,1,2,9,56,480,5094,65534,984808,16629264, 312523680,6425601072,143775827832,3471659156784, 90060216241800,2496918043296840,73703868906725184, 2307477802376274048,76376765284713220032, 2664806795257276548288,97747916619062963335680] |