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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 26 |
| 4 | 292 |
| 5 | 3468 |
| 6 | 69664 |
| 7 | 1208936 |
| 8 | 32822456 |
| 9 | 858979216 |
| 10 | 28933584112 |
| 11 | 836115182512 |
| 12 | 40673697842208 |
| 13 | 1381857061152896 |
| 14 | 67261437417875776 |
| 15 | 3297904559465926208 |
| 16 | 192628214559932492928 |
| 17 | 8815748379077085483264 |
[1,1,4,26,292,3468,69664,1208936,32822456, 858979216,28933584112,836115182512,40673697842208, 1381857061152896,67261437417875776, 3297904559465926208,192628214559932492928, 8815748379077085483264] |