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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 9 |
| 3 | 57 |
| 4 | 411 |
| 5 | 3150 |
| 6 | 25274 |
| 7 | 209719 |
| 8 | 1784909 |
| 9 | 15495058 |
| 10 | 136672624 |
| 11 | 1221370092 |
| 12 | 11034687854 |
| 13 | 100623850938 |
| 14 | 924917387599 |
| 15 | 8560734224711 |
| 16 | 79717622732369 |
| 17 | 746322905220237 |
| 18 | 7020573752016609 |
| 19 | 66324819580927731 |
| 20 | 629004053328092981 |
[1,2,9,57,411,3150,25274,209719,1784909,15495058, 136672624,1221370092,11034687854,100623850938, 924917387599,8560734224711,79717622732369, 746322905220237,7020573752016609, 66324819580927731,629004053328092981] |