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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 23 |
| 4 | 139 |
| 5 | 860 |
| 6 | 5393 |
| 7 | 34142 |
| 8 | 217717 |
| 9 | 1396346 |
| 10 | 8997695 |
| 11 | 58205686 |
| 12 | 377775385 |
| 13 | 2458841504 |
| 14 | 16043226825 |
| 15 | 104901986083 |
| 16 | 687221188145 |
| 17 | 4509605878736 |
| 18 | 29636894936761 |
| 19 | 195035340954186 |
| 20 | 1285062484293880 |
| 21 | 8476508261617168 |
| 22 | 55969236979211755 |
| 23 | 369900194873712830 |
[1,1,4,23,139,860,5393,34142,217717,1396346, 8997695,58205686,377775385,2458841504,16043226825, 104901986083,687221188145,4509605878736, 29636894936761,195035340954186,1285062484293880, 8476508261617168,55969236979211755, 369900194873712830] |