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| n | a(n) |
|---|---|
| 0 | 21 |
| 1 | 56 |
| 2 | 196 |
| 3 | 812 |
| 4 | 3724 |
| 5 | 18236 |
| 6 | 93436 |
| 7 | 494732 |
| 8 | 2685004 |
| 9 | 14851676 |
| 10 | 83384476 |
| 11 | 473755052 |
| 12 | 2717541484 |
| 13 | 15709845116 |
| 14 | 91395715516 |
| 15 | 534498925772 |
| 16 | 3139343105164 |
| 17 | 18504595174556 |
| 18 | 109397060622556 |
| 19 | 648335998054892 |
| 20 | 3850205790608044 |
[21,56,196,812,3724,18236,93436,494732,2685004, 14851676,83384476,473755052,2717541484, 15709845116,91395715516,534498925772, 3139343105164,18504595174556,109397060622556, 648335998054892,3850205790608044] |