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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 2 |
| 3 | 7 |
| 4 | 20 |
| 5 | 52 |
| 6 | 144 |
| 7 | 389 |
| 8 | 1058 |
| 9 | 2876 |
| 10 | 7817 |
| 11 | 21250 |
| 12 | 57763 |
| 13 | 157017 |
| 14 | 426817 |
| 15 | 1160207 |
| 16 | 3153770 |
| 17 | 8572836 |
| 18 | 23303385 |
| 19 | 63345169 |
| 20 | 172190019 |
| 21 | 468061001 |
| 22 | 1272321714 |
| 23 | 3458528995 |
| 24 | 9401256521 |
| 25 | 25555264765 |
| 26 | 69466411833 |
| 27 | 188829284972 |
[0,1,2,7,20,52,144,389,1058,2876,7817,21250,57763, 157017,426817,1160207,3153770,8572836,23303385, 63345169,172190019,468061001,1272321714, 3458528995,9401256521,25555264765,69466411833, 188829284972] |