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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 4 |
| 3 | 16 |
| 4 | 94 |
| 5 | 718 |
| 6 | 6698 |
| 7 | 73512 |
| 8 | 925944 |
| 9 | 13149408 |
| 10 | 207723792 |
| 11 | 3611861856 |
| 12 | 68535403440 |
| 13 | 1409110979664 |
| 14 | 31203828680880 |
| 15 | 740391021216384 |
| 16 | 18739539315968256 |
| 17 | 503958517859488896 |
| 18 | 14350254992824182912 |
| 19 | 431329037106221865216 |
| 20 | 13646963521734433991424 |
[1,2,4,16,94,718,6698,73512,925944,13149408, 207723792,3611861856,68535403440,1409110979664, 31203828680880,740391021216384,18739539315968256, 503958517859488896,14350254992824182912, 431329037106221865216,13646963521734433991424] |