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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 4 |
| 4 | 13 |
| 5 | 68 |
| 6 | 373 |
| 7 | 2472 |
| 8 | 18649 |
| 9 | 152144 |
| 10 | 1433129 |
| 11 | 14034560 |
| 12 | 156563045 |
| 13 | 1799730624 |
| 14 | 23043285021 |
| 15 | 304857999232 |
| 16 | 4392102360241 |
| 17 | 65741679927552 |
| 18 | 1051530622359889 |
| 19 | 17551668357299200 |
| 20 | 308633929353801661 |
[1,1,1,4,13,68,373,2472,18649,152144,1433129, 14034560,156563045,1799730624,23043285021, 304857999232,4392102360241,65741679927552, 1051530622359889,17551668357299200, 308633929353801661] |