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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 18 |
| 2 | 252 |
| 3 | 3240 |
| 4 | 40176 |
| 5 | 489888 |
| 6 | 5925312 |
| 7 | 71383680 |
| 8 | 858283776 |
| 9 | 10309483008 |
| 10 | 123774262272 |
| 11 | 1485653944320 |
| 12 | 17830024114176 |
| 13 | 213973350064128 |
| 14 | 2567758564933632 |
| 15 | 30813572964188160 |
| 16 | 369765696680165376 |
| 17 | 4437205286821429248 |
| 18 | 53246565001813819392 |
| 19 | 638959389381505843200 |
| 20 | 7667516328736510181376 |
| 21 | 92010217881788762554368 |
[1,18,252,3240,40176,489888,5925312,71383680, 858283776,10309483008,123774262272,1485653944320, 17830024114176,213973350064128,2567758564933632, 30813572964188160,369765696680165376, 4437205286821429248,53246565001813819392, 638959389381505843200,7667516328736510181376, 92010217881788762554368] |