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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 3 |
| 3 | 10 |
| 4 | 33 |
| 5 | 109 |
| 6 | 360 |
| 7 | 1189 |
| 8 | 3927 |
| 9 | 12970 |
| 10 | 42837 |
| 11 | 141481 |
| 12 | 467280 |
| 13 | 1543321 |
| 14 | 5097243 |
| 15 | 16835050 |
| 16 | 55602393 |
| 17 | 183642229 |
| 18 | 606529080 |
| 19 | 2003229469 |
| 20 | 6616217487 |
| 21 | 21851881930 |
| 22 | 72171863277 |
| 23 | 238367471761 |
| 24 | 787274278560 |
| 25 | 2600190307441 |
[0,1,3,10,33,109,360,1189,3927,12970,42837,141481, 467280,1543321,5097243,16835050,55602393, 183642229,606529080,2003229469,6616217487, 21851881930,72171863277,238367471761,787274278560, 2600190307441] |