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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 32 |
| 3 | 286 |
| 4 | 2688 |
| 5 | 26004 |
| 6 | 256322 |
| 7 | 2559960 |
| 8 | 25816576 |
| 9 | 262307824 |
| 10 | 2681024032 |
| 11 | 27534988936 |
| 12 | 283926200706 |
| 13 | 2937573629800 |
| 14 | 30480431060160 |
| 15 | 317053438632786 |
| 16 | 3305105501423616 |
| 17 | 34519689280675808 |
| 18 | 361146528603877520 |
| 19 | 3784045825018539968 |
| 20 | 39702608870540290688 |
[1,4,32,286,2688,26004,256322,2559960,25816576, 262307824,2681024032,27534988936,283926200706, 2937573629800,30480431060160,317053438632786, 3305105501423616,34519689280675808, 361146528603877520,3784045825018539968, 39702608870540290688] |