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| n | a(n) |
|---|---|
| 1 | 4 |
| 2 | 25 |
| 3 | 148 |
| 4 | 884 |
| 5 | 5296 |
| 6 | 31760 |
| 7 | 190528 |
| 8 | 1143104 |
| 9 | 6858496 |
| 10 | 41150720 |
| 11 | 246903808 |
| 12 | 1481421824 |
| 13 | 8888528896 |
| 14 | 53331169280 |
| 15 | 319987007488 |
| 16 | 1919922028544 |
| 17 | 11519532138496 |
| 18 | 69117192765440 |
| 19 | 414703156461568 |
| 20 | 2488218938507264 |
[4,25,148,884,5296,31760,190528,1143104,6858496, 41150720,246903808,1481421824,8888528896, 53331169280,319987007488,1919922028544, 11519532138496,69117192765440,414703156461568, 2488218938507264] |