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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 7 |
| 4 | 28 |
| 5 | 138 |
| 6 | 818 |
| 7 | 5658 |
| 8 | 44784 |
| 9 | 399366 |
| 10 | 3962256 |
| 11 | 43289760 |
| 12 | 516432984 |
| 13 | 6679346280 |
| 14 | 93091875120 |
| 15 | 1390851720840 |
| 16 | 22175338353120 |
| 17 | 375794883339120 |
| 18 | 6745177713093840 |
| 19 | 127830886641354960 |
| 20 | 2550687440585679360 |
| 21 | 53451172032327664560 |
| 22 | 1173650135526055272960 |
[1,1,2,7,28,138,818,5658,44784,399366,3962256, 43289760,516432984,6679346280,93091875120, 1390851720840,22175338353120,375794883339120, 6745177713093840,127830886641354960, 2550687440585679360,53451172032327664560, 1173650135526055272960] |