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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 4 |
| 3 | 12 |
| 4 | 36 |
| 5 | 120 |
| 6 | 462 |
| 7 | 2058 |
| 8 | 10472 |
| 9 | 59976 |
| 10 | 381770 |
| 11 | 2673374 |
| 12 | 20422908 |
| 13 | 169020852 |
| 14 | 1506427678 |
| 15 | 14385323610 |
| 16 | 146527700944 |
| 17 | 1585801332848 |
| 18 | 18171944693586 |
| 19 | 219803766565366 |
| 20 | 2798628476670180 |
| 21 | 37414906698747564 |
| 22 | 524019526485293894 |
| 23 | 7672827408344428242 |
[0,1,4,12,36,120,462,2058,10472,59976,381770, 2673374,20422908,169020852,1506427678,14385323610, 146527700944,1585801332848,18171944693586, 219803766565366,2798628476670180, 37414906698747564,524019526485293894, 7672827408344428242] |