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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 1 |
| 3 | 2 |
| 4 | 7 |
| 5 | 24 |
| 6 | 91 |
| 7 | 354 |
| 8 | 1491 |
| 9 | 6504 |
| 10 | 29711 |
| 11 | 139616 |
| 12 | 674696 |
| 13 | 3328798 |
| 14 | 16730955 |
| 15 | 85382210 |
| 16 | 441571216 |
| 17 | 2310003732 |
| 18 | 12206975528 |
| 19 | 65082858008 |
| 20 | 349756996762 |
| 21 | 1892980028014 |
| 22 | 10310987833049 |
| 23 | 56489307860860 |
| 24 | 311112321625754 |
| 25 | 1721692801914844 |
| 26 | 9569930999155801 |
| 27 | 53410232801675436 |
[0,1,2,7,24,91,354,1491,6504,29711,139616,674696, 3328798,16730955,85382210,441571216,2310003732, 12206975528,65082858008,349756996762, 1892980028014,10310987833049,56489307860860, 311112321625754,1721692801914844,9569930999155801, 53410232801675436] |