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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 0 |
| 3 | 1 |
| 4 | 2 |
| 5 | 6 |
| 6 | 21 |
| 7 | 65 |
| 8 | 221 |
| 9 | 771 |
| 10 | 2769 |
| 11 | 10250 |
| 12 | 39243 |
| 13 | 154658 |
| 14 | 628635 |
| 15 | 2632420 |
| 16 | 11353457 |
| 17 | 50411413 |
| 18 | 230341716 |
| 19 | 1082481189 |
| 20 | 5228952960 |
| 21 | 25945377057 |
| 22 | 132140242356 |
| 23 | 690238318754 |
| 24 | 3694876952577 |
| 25 | 20252697246580 |
| 26 | 113578669178222 |
| 27 | 651178533855913 |
| 28 | 3813856010041981 |
[1,0,0,1,2,6,21,65,221,771,2769,10250,39243, 154658,628635,2632420,11353457,50411413,230341716, 1082481189,5228952960,25945377057,132140242356, 690238318754,3694876952577,20252697246580, 113578669178222,651178533855913,3813856010041981] |