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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 3 |
| 3 | 17 |
| 4 | 132 |
| 5 | 1334 |
| 6 | 16442 |
| 7 | 239994 |
| 8 | 4041776 |
| 9 | 77183328 |
| 10 | 1647541632 |
| 11 | 38877352392 |
| 12 | 1004869488048 |
| 13 | 28234217634024 |
| 14 | 856830099396840 |
| 15 | 27930093941047464 |
| 16 | 973269467390922240 |
| 17 | 36104568839480990400 |
| 18 | 1420556927968241858880 |
| 19 | 59088101641333114906944 |
| 20 | 2590680379402887359111424 |
[1,1,3,17,132,1334,16442,239994,4041776,77183328, 1647541632,38877352392,1004869488048, 28234217634024,856830099396840,27930093941047464, 973269467390922240,36104568839480990400, 1420556927968241858880,59088101641333114906944, 2590680379402887359111424] |