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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 16 |
| 3 | 56 |
| 4 | 172 |
| 5 | 496 |
| 6 | 1360 |
| 7 | 3528 |
| 8 | 8824 |
| 9 | 21344 |
| 10 | 50048 |
| 11 | 114360 |
| 12 | 255336 |
| 13 | 557888 |
| 14 | 1195952 |
| 15 | 2519264 |
| 16 | 5221076 |
| 17 | 10660512 |
| 18 | 21467904 |
| 19 | 42674520 |
| 20 | 83812560 |
| 21 | 162753584 |
| 22 | 312689168 |
| 23 | 594740456 |
| 24 | 1120498048 |
| 25 | 2092059800 |
| 26 | 3872731232 |
| 27 | 7110830376 |
| 28 | 12955269304 |
| 29 | 23428775520 |
[1,4,16,56,172,496,1360,3528,8824,21344,50048, 114360,255336,557888,1195952,2519264,5221076, 10660512,21467904,42674520,83812560,162753584, 312689168,594740456,1120498048,2092059800, 3872731232,7110830376,12955269304,23428775520] |