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| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 16 |
| 3 | 90 |
| 4 | 603 |
| 5 | 3445 |
| 6 | 15789 |
| 7 | 98224 |
| 8 | 645217 |
| 9 | 3227100 |
| 10 | 18747520 |
| 11 | 128798244 |
| 12 | 720878886 |
| 13 | 4180036645 |
| 14 | 28917238756 |
| 15 | 176708726320 |
| 16 | 1057330250552 |
| 17 | 7322809072734 |
| 18 | 47678383274385 |
| 19 | 297647051017140 |
| 20 | 2072720881428948 |
[2,16,90,603,3445,15789,98224,645217,3227100, 18747520,128798244,720878886,4180036645, 28917238756,176708726320,1057330250552, 7322809072734,47678383274385,297647051017140, 2072720881428948] |