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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 16 |
| 4 | 76 |
| 5 | 436 |
| 6 | 2776 |
| 7 | 19384 |
| 8 | 148576 |
| 9 | 1226656 |
| 10 | 10824256 |
| 11 | 101695936 |
| 12 | 1010783104 |
| 13 | 10577428096 |
| 14 | 116166090496 |
| 15 | 1334409569536 |
| 16 | 15985101216256 |
| 17 | 199216504113664 |
| 18 | 2577292524107776 |
| 19 | 34542575915216896 |
| 20 | 478781761481291776 |
[1,1,4,16,76,436,2776,19384,148576,1226656, 10824256,101695936,1010783104,10577428096, 116166090496,1334409569536,15985101216256, 199216504113664,2577292524107776, 34542575915216896,478781761481291776] |