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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 25 |
| 5 | 123 |
| 6 | 683 |
| 7 | 4083 |
| 8 | 25839 |
| 9 | 171324 |
| 10 | 1178755 |
| 11 | 8362768 |
| 12 | 60867478 |
| 13 | 452760486 |
| 14 | 3431366195 |
| 15 | 26430813268 |
| 16 | 206504120774 |
| 17 | 1633813641572 |
| 18 | 13071700375914 |
| 19 | 105635826348216 |
| 20 | 861408409243195 |
| 21 | 7081998941608535 |
| 22 | 58658594339423251 |
| 23 | 489168002223876023 |
| 24 | 4104791591982736028 |
[1,1,2,6,25,123,683,4083,25839,171324,1178755, 8362768,60867478,452760486,3431366195,26430813268, 206504120774,1633813641572,13071700375914, 105635826348216,861408409243195,7081998941608535, 58658594339423251,489168002223876023, 4104791591982736028] |