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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 19 |
| 4 | 132 |
| 5 | 1119 |
| 6 | 12057 |
| 7 | 151560 |
| 8 | 2234970 |
| 9 | 37355130 |
| 10 | 702161460 |
| 11 | 14608747440 |
| 12 | 333760916475 |
| 13 | 8297318063475 |
| 14 | 223043540630400 |
| 15 | 6444290305953675 |
| 16 | 199158606533605950 |
| 17 | 6554872218153191625 |
| 18 | 228899544451085017125 |
| 19 | 8452452568601816775000 |
| 20 | 329069272855540304587500 |
[1,1,4,19,132,1119,12057,151560,2234970,37355130, 702161460,14608747440,333760916475,8297318063475, 223043540630400,6444290305953675, 199158606533605950,6554872218153191625, 228899544451085017125,8452452568601816775000, 329069272855540304587500] |