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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 6 |
| 3 | 24 |
| 4 | 121 |
| 5 | 598 |
| 6 | 3047 |
| 7 | 15696 |
| 8 | 81981 |
| 9 | 432491 |
| 10 | 2302608 |
| 11 | 12355260 |
| 12 | 66761159 |
| 13 | 362992938 |
| 14 | 1984748322 |
| 15 | 10907074884 |
| 16 | 60215001180 |
| 17 | 333824553431 |
| 18 | 1857784353244 |
| 19 | 10375296176688 |
| 20 | 58131888133855 |
| 21 | 326686361277196 |
| 22 | 1841007865239913 |
[1,6,24,121,598,3047,15696,81981,432491,2302608, 12355260,66761159,362992938,1984748322, 10907074884,60215001180,333824553431, 1857784353244,10375296176688,58131888133855, 326686361277196,1841007865239913] |