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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 3 |
| 3 | 18 |
| 4 | 157 |
| 5 | 1776 |
| 6 | 24807 |
| 7 | 413344 |
| 8 | 8004537 |
| 9 | 176630400 |
| 10 | 4374300331 |
| 11 | 120136735104 |
| 12 | 3623854678677 |
| 13 | 119102912981248 |
| 14 | 4236492477409935 |
| 15 | 162152320065532416 |
| 16 | 6645233337842716273 |
| 17 | 290321208589666369536 |
| 18 | 13469914225467040015827 |
| 19 | 661442143465113960448000 |
[1,1,3,18,157,1776,24807,413344,8004537,176630400, 4374300331,120136735104,3623854678677, 119102912981248,4236492477409935, 162152320065532416,6645233337842716273, 290321208589666369536,13469914225467040015827, 661442143465113960448000] |