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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 28 |
| 3 | 260 |
| 4 | 2916 |
| 5 | 37712 |
| 6 | 547240 |
| 7 | 8751688 |
| 8 | 152309648 |
| 9 | 2857598164 |
| 10 | 57379111732 |
| 11 | 1225920973324 |
| 12 | 27737038620452 |
| 13 | 661937827915872 |
| 14 | 16605857832896944 |
| 15 | 436636765049489648 |
| 16 | 12002769920717089856 |
| 17 | 344160801015503753892 |
[1,4,28,260,2916,37712,547240,8751688,152309648, 2857598164,57379111732,1225920973324, 27737038620452,661937827915872,16605857832896944, 436636765049489648,12002769920717089856, 344160801015503753892] |