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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 38 |
| 4 | 576 |
| 5 | 12052 |
| 6 | 322848 |
| 7 | 10564304 |
| 8 | 408903680 |
| 9 | 18288706544 |
| 10 | 928575662400 |
| 11 | 52780935007968 |
| 12 | 3321208845997056 |
| 13 | 229232635832433664 |
| 14 | 17221699990084108288 |
| 15 | 1399139700462119135232 |
| 16 | 122235936429355565580288 |
| 17 | 11428226675376971405577984 |
| 18 | 1138551595285580854471388160 |
[1,1,4,38,576,12052,322848,10564304,408903680, 18288706544,928575662400,52780935007968, 3321208845997056,229232635832433664, 17221699990084108288,1399139700462119135232, 122235936429355565580288, 11428226675376971405577984, 1138551595285580854471388160] |