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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 16 |
| 4 | 45 |
| 5 | 132 |
| 6 | 399 |
| 7 | 1240 |
| 8 | 3951 |
| 9 | 12870 |
| 10 | 42746 |
| 11 | 144420 |
| 12 | 495300 |
| 13 | 1721202 |
| 14 | 6051150 |
| 15 | 21493136 |
| 16 | 77039070 |
| 17 | 278377452 |
| 18 | 1013187920 |
| 19 | 3711505380 |
| 20 | 13675028346 |
| 21 | 50649452084 |
| 22 | 188482525039 |
| 23 | 704409735912 |
| 24 | 2642825539375 |
| 25 | 9950643710800 |
| 26 | 37587291143103 |
| 27 | 142403408032648 |
[1,2,6,16,45,132,399,1240,3951,12870,42746,144420, 495300,1721202,6051150,21493136,77039070, 278377452,1013187920,3711505380,13675028346, 50649452084,188482525039,704409735912, 2642825539375,9950643710800,37587291143103, 142403408032648] |