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| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 2 |
| 3 | 6 |
| 4 | 16 |
| 5 | 65 |
| 6 | 312 |
| 7 | 1813 |
| 8 | 12288 |
| 9 | 95617 |
| 10 | 840960 |
| 11 | 8254081 |
| 12 | 89441280 |
| 13 | 1060369921 |
| 14 | 13649610240 |
| 15 | 189550368001 |
| 16 | 2824077312000 |
| 17 | 44927447040001 |
| 18 | 760034451456000 |
| 19 | 13622700994560001 |
| 20 | 257872110354432000 |
| 21 | 5140559166898176001 |
[2,2,6,16,65,312,1813,12288,95617,840960,8254081, 89441280,1060369921,13649610240,189550368001, 2824077312000,44927447040001,760034451456000, 13622700994560001,257872110354432000, 5140559166898176001] |