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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 16 |
| 3 | 64 |
| 4 | 252 |
| 5 | 968 |
| 6 | 3616 |
| 7 | 13120 |
| 8 | 46432 |
| 9 | 160772 |
| 10 | 545856 |
| 11 | 1821056 |
| 12 | 5979520 |
| 13 | 19350552 |
| 14 | 61795968 |
| 15 | 194964672 |
| 16 | 608261628 |
| 17 | 1878140024 |
| 18 | 5743681784 |
| 19 | 17408223328 |
| 20 | 52320105080 |
| 21 | 156011658272 |
| 22 | 461763417056 |
| 23 | 1357182242560 |
| 24 | 3962591708576 |
| 25 | 11497241014652 |
[1,4,16,64,252,968,3616,13120,46432,160772,545856, 1821056,5979520,19350552,61795968,194964672, 608261628,1878140024,5743681784,17408223328, 52320105080,156011658272,461763417056, 1357182242560,3962591708576,11497241014652] |