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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 17 |
| 3 | 72 |
| 4 | 305 |
| 5 | 1300 |
| 6 | 5576 |
| 7 | 24068 |
| 8 | 104510 |
| 9 | 456332 |
| 10 | 2002675 |
| 11 | 8829892 |
| 12 | 39096653 |
| 13 | 173781548 |
| 14 | 775183764 |
| 15 | 3469084436 |
| 16 | 15571135682 |
| 17 | 70084045640 |
| 18 | 316242702258 |
| 19 | 1430351652352 |
| 20 | 6483550388522 |
| 21 | 29448610671464 |
| 22 | 134010580021152 |
[1,4,17,72,305,1300,5576,24068,104510,456332, 2002675,8829892,39096653,173781548,775183764, 3469084436,15571135682,70084045640,316242702258, 1430351652352,6483550388522,29448610671464, 134010580021152] |