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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 4 |
| 3 | 9 |
| 4 | 24 |
| 5 | 72 |
| 6 | 225 |
| 7 | 702 |
| 8 | 2160 |
| 9 | 6561 |
| 10 | 19764 |
| 11 | 59292 |
| 12 | 177633 |
| 13 | 532170 |
| 14 | 1595052 |
| 15 | 4782969 |
| 16 | 14346720 |
| 17 | 43040160 |
| 18 | 129127041 |
| 19 | 387400806 |
| 20 | 1162241784 |
| 21 | 3486784401 |
| 22 | 10460412252 |
| 23 | 31381236756 |
| 24 | 94143533121 |
| 25 | 282430067922 |
| 26 | 847289140884 |
| 27 | 2541865828329 |
| 28 | 7625595890664 |
[1,2,4,9,24,72,225,702,2160,6561,19764,59292, 177633,532170,1595052,4782969,14346720,43040160, 129127041,387400806,1162241784,3486784401, 10460412252,31381236756,94143533121,282430067922, 847289140884,2541865828329,7625595890664] |