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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 4 |
| 3 | 9 |
| 4 | 24 |
| 5 | 78 |
| 6 | 317 |
| 7 | 1636 |
| 8 | 10752 |
| 9 | 89871 |
| 10 | 955536 |
| 11 | 12930172 |
| 12 | 222618065 |
| 13 | 4874855542 |
| 14 | 135781292308 |
| 15 | 4811103270053 |
| 16 | 216847500834512 |
| 17 | 12432143862756778 |
| 18 | 906625645142897789 |
| 19 | 84102571511631809864 |
| 20 | 9923979699312024569440 |
| 21 | 1489546408205976627946331 |
[1,2,4,9,24,78,317,1636,10752,89871,955536, 12930172,222618065,4874855542,135781292308, 4811103270053,216847500834512,12432143862756778, 906625645142897789,84102571511631809864, 9923979699312024569440,1489546408205976627946331] |