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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 1 |
| 3 | 2 |
| 4 | 9 |
| 5 | 44 |
| 6 | 265 |
| 7 | 1854 |
| 8 | 10860 |
| 9 | 55314 |
| 10 | 259285 |
| 11 | 1178912 |
| 12 | 5382017 |
| 13 | 25157980 |
| 14 | 121727936 |
| 15 | 598440744 |
| 16 | 2954197380 |
| 17 | 14540741660 |
| 18 | 71135825805 |
| 19 | 345881286126 |
| 20 | 1675123912129 |
| 21 | 8108391695252 |
| 22 | 39291412775944 |
| 23 | 190687692089500 |
| 24 | 926601640342609 |
| 25 | 4505656310652572 |
[1,0,1,2,9,44,265,1854,10860,55314,259285,1178912, 5382017,25157980,121727936,598440744,2954197380, 14540741660,71135825805,345881286126, 1675123912129,8108391695252,39291412775944, 190687692089500,926601640342609,4505656310652572] |