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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 27 |
| 4 | 260 |
| 5 | 3280 |
| 6 | 51414 |
| 7 | 965762 |
| 8 | 21175496 |
| 9 | 531317520 |
| 10 | 15021531840 |
| 11 | 472654558992 |
| 12 | 16385500397496 |
| 13 | 620612495460048 |
| 14 | 25500923655523848 |
| 15 | 1129909190812470840 |
| 16 | 53705490284841870144 |
| 17 | 2725878142900911376896 |
[1,1,4,27,260,3280,51414,965762,21175496, 531317520,15021531840,472654558992,16385500397496, 620612495460048,25500923655523848, 1129909190812470840,53705490284841870144, 2725878142900911376896] |