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| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 0 |
| 3 | 1 |
| 4 | 15 |
| 5 | 65 |
| 6 | 202 |
| 7 | 537 |
| 8 | 1559 |
| 9 | 6506 |
| 10 | 27557 |
| 11 | 104122 |
| 12 | 360598 |
| 13 | 1236670 |
| 14 | 4479897 |
| 15 | 16998081 |
| 16 | 64623235 |
| 17 | 240399786 |
| 18 | 880495525 |
| 19 | 3233751496 |
| 20 | 12035510317 |
| 21 | 45240963675 |
| 22 | 170207777737 |
| 23 | 637838570111 |
| 24 | 2384646622991 |
| 25 | 8931032553574 |
[2,0,1,15,65,202,537,1559,6506,27557,104122, 360598,1236670,4479897,16998081,64623235, 240399786,880495525,3233751496,12035510317, 45240963675,170207777737,637838570111, 2384646622991,8931032553574] |