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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 0 |
| 3 | 1 |
| 4 | 2 |
| 5 | 6 |
| 6 | 16 |
| 7 | 43 |
| 8 | 117 |
| 9 | 319 |
| 10 | 875 |
| 11 | 2409 |
| 12 | 6692 |
| 13 | 18614 |
| 14 | 52099 |
| 15 | 146186 |
| 16 | 411720 |
| 17 | 1162295 |
| 18 | 3289994 |
| 19 | 9330913 |
| 20 | 26517036 |
| 21 | 75481622 |
| 22 | 215201178 |
| 23 | 614398459 |
| 24 | 1756392061 |
| 25 | 5026955216 |
| 26 | 14403488345 |
| 27 | 41311616835 |
| 28 | 118601561506 |
| 29 | 340795908579 |
| 30 | 980078195995 |
[0,0,0,1,2,6,16,43,117,319,875,2409,6692,18614, 52099,146186,411720,1162295,3289994,9330913, 26517036,75481622,215201178,614398459,1756392061, 5026955216,14403488345,41311616835,118601561506, 340795908579,980078195995] |