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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 16 |
| 3 | 100 |
| 4 | 832 |
| 5 | 8644 |
| 6 | 107776 |
| 7 | 1567780 |
| 8 | 26063872 |
| 9 | 487466884 |
| 10 | 10129985536 |
| 11 | 231560895460 |
| 12 | 5774444019712 |
| 13 | 155997355725124 |
| 14 | 4538464905527296 |
| 15 | 141469868440031140 |
| 16 | 4703786933664612352 |
| 17 | 166172927821116399364 |
| 18 | 6215792183431115309056 |
| 19 | 245422172388559255422820 |
[1,4,16,100,832,8644,107776,1567780,26063872, 487466884,10129985536,231560895460,5774444019712, 155997355725124,4538464905527296, 141469868440031140,4703786933664612352, 166172927821116399364,6215792183431115309056, 245422172388559255422820] |