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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 1 |
| 3 | 2 |
| 4 | 9 |
| 5 | 24 |
| 6 | 97 |
| 7 | 314 |
| 8 | 1285 |
| 9 | 4740 |
| 10 | 20161 |
| 11 | 81782 |
| 12 | 364037 |
| 13 | 1590768 |
| 14 | 7415361 |
| 15 | 34458418 |
| 16 | 167934917 |
| 17 | 822644860 |
| 18 | 4181343201 |
| 19 | 21456885262 |
| 20 | 113446435685 |
| 21 | 606954796712 |
| 22 | 3329669253153 |
| 23 | 18503539170954 |
| 24 | 105074939752933 |
| 25 | 604670497368692 |
| 26 | 3546768810450817 |
| 27 | 21082213234142886 |
[0,0,1,2,9,24,97,314,1285,4740,20161,81782,364037, 1590768,7415361,34458418,167934917,822644860, 4181343201,21456885262,113446435685,606954796712, 3329669253153,18503539170954,105074939752933, 604670497368692,3546768810450817, 21082213234142886] |