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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 4 |
| 3 | 16 |
| 4 | 76 |
| 5 | 436 |
| 6 | 2956 |
| 7 | 23116 |
| 8 | 204556 |
| 9 | 2018956 |
| 10 | 21977356 |
| 11 | 261478156 |
| 12 | 3374988556 |
| 13 | 46964134156 |
| 14 | 700801318156 |
| 15 | 11162196262156 |
| 16 | 189005910310156 |
| 17 | 3390192763174156 |
| 18 | 64212742967590156 |
| 19 | 1280663747055910156 |
| 20 | 26826134832910630156 |
| 21 | 588826498721714470156 |
[1,4,16,76,436,2956,23116,204556,2018956,21977356, 261478156,3374988556,46964134156,700801318156, 11162196262156,189005910310156,3390192763174156, 64212742967590156,1280663747055910156, 26826134832910630156,588826498721714470156] |