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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 4 |
| 4 | 12 |
| 5 | 40 |
| 6 | 154 |
| 7 | 656 |
| 8 | 3074 |
| 9 | 15616 |
| 10 | 85360 |
| 11 | 498464 |
| 12 | 3092450 |
| 13 | 20286360 |
| 14 | 140153382 |
| 15 | 1016262080 |
| 16 | 7710988372 |
| 17 | 61062381784 |
| 18 | 503482376930 |
| 19 | 4313580705728 |
| 20 | 38328590370762 |
| 21 | 352618807559008 |
| 22 | 3353663977088848 |
| 23 | 32927374589861296 |
[1,2,4,12,40,154,656,3074,15616,85360,498464, 3092450,20286360,140153382,1016262080,7710988372, 61062381784,503482376930,4313580705728, 38328590370762,352618807559008,3353663977088848, 32927374589861296] |