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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 16 |
| 4 | 81 |
| 5 | 400 |
| 6 | 2304 |
| 7 | 13225 |
| 8 | 81796 |
| 9 | 516961 |
| 10 | 3392964 |
| 11 | 22714756 |
| 12 | 155900196 |
| 13 | 1087218729 |
| 14 | 7710771721 |
| 15 | 55404215161 |
| 16 | 403030713409 |
| 17 | 2962388303281 |
| 18 | 21983682632976 |
| 19 | 164512124707984 |
| 20 | 1240577449436224 |
[1,1,4,16,81,400,2304,13225,81796,516961,3392964, 22714756,155900196,1087218729,7710771721, 55404215161,403030713409,2962388303281, 21983682632976,164512124707984,1240577449436224] |