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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 6 |
| 2 | 30 |
| 3 | 144 |
| 4 | 690 |
| 5 | 3348 |
| 6 | 16536 |
| 7 | 83232 |
| 8 | 426618 |
| 9 | 2223180 |
| 10 | 11756052 |
| 11 | 62959680 |
| 12 | 340881792 |
| 13 | 1862954784 |
| 14 | 10262937600 |
| 15 | 56926831104 |
| 16 | 317632207194 |
| 17 | 1781352834300 |
| 18 | 10034760283356 |
| 19 | 56748881420640 |
| 20 | 322033934657628 |
| 21 | 1833043230774360 |
| 22 | 10462349697348528 |
| 23 | 59861990921495616 |
[1,6,30,144,690,3348,16536,83232,426618,2223180, 11756052,62959680,340881792,1862954784, 10262937600,56926831104,317632207194, 1781352834300,10034760283356,56748881420640, 322033934657628,1833043230774360, 10462349697348528,59861990921495616] |