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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 21 |
| 2 | 336 |
| 3 | 4536 |
| 4 | 54432 |
| 5 | 598752 |
| 6 | 6158592 |
| 7 | 60046272 |
| 8 | 560431872 |
| 9 | 5043886848 |
| 10 | 44019376128 |
| 11 | 374164697088 |
| 12 | 3108445175808 |
| 13 | 25311625003008 |
| 14 | 202493000024064 |
| 15 | 1594632375189504 |
| 16 | 12381851383824384 |
| 17 | 94927527275986944 |
[1,21,336,4536,54432,598752,6158592,60046272, 560431872,5043886848,44019376128,374164697088, 3108445175808,25311625003008,202493000024064, 1594632375189504,12381851383824384, 94927527275986944] |