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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 16 |
| 5 | 72 |
| 6 | 288 |
| 7 | 1848 |
| 8 | 9920 |
| 9 | 81088 |
| 10 | 541184 |
| 11 | 5318016 |
| 12 | 42274816 |
| 13 | 483162240 |
| 14 | 4449451776 |
| 15 | 57865303296 |
| 16 | 605255720960 |
| 17 | 8815813734400 |
| 18 | 103187353223168 |
| 19 | 1662921003208704 |
| 20 | 21528004660707328 |
| 21 | 380141599264751616 |
| 22 | 5391886872902762496 |
| 23 | 103492751953073897472 |
[0,1,2,6,16,72,288,1848,9920,81088,541184,5318016, 42274816,483162240,4449451776,57865303296, 605255720960,8815813734400,103187353223168, 1662921003208704,21528004660707328, 380141599264751616,5391886872902762496, 103492751953073897472] |