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| n | a(n) |
|---|---|
| -1 | 1 |
| 0 | 1 |
| 1 | 2 |
| 2 | 4 |
| 3 | 11 |
| 4 | 30 |
| 5 | 103 |
| 6 | 354 |
| 7 | 1440 |
| 8 | 5911 |
| 9 | 27651 |
| 10 | 131062 |
| 11 | 690543 |
| 12 | 3693765 |
| 13 | 21585068 |
| 14 | 128165652 |
| 15 | 820859645 |
| 16 | 5343318222 |
| 17 | 37155889171 |
| 18 | 262577578134 |
| 19 | 1967281479508 |
| 20 | 14975397597557 |
| 21 | 120122032987319 |
| 22 | 978625889818014 |
| 23 | 8359402026954939 |
| 24 | 72495015037575673 |
| 25 | 656446920912518700 |
[1,1,2,4,11,30,103,354,1440,5911,27651,131062, 690543,3693765,21585068,128165652,820859645, 5343318222,37155889171,262577578134,1967281479508, 14975397597557,120122032987319,978625889818014, 8359402026954939,72495015037575673, 656446920912518700] |