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| n | a(n) |
|---|---|
| 1 | 4 |
| 2 | 31 |
| 3 | 126 |
| 4 | 575 |
| 5 | 2832 |
| 6 | 13322 |
| 7 | 62874 |
| 8 | 299056 |
| 9 | 1418177 |
| 10 | 6723333 |
| 11 | 31896327 |
| 12 | 151295253 |
| 13 | 717601109 |
| 14 | 3403806391 |
| 15 | 16145223273 |
| 16 | 76580830416 |
| 17 | 363243440911 |
| 18 | 1722961426119 |
| 19 | 8172464117705 |
| 20 | 38764179352078 |
| 21 | 183868863324799 |
| 22 | 872139110880993 |
[4,31,126,575,2832,13322,62874,299056,1418177, 6723333,31896327,151295253,717601109,3403806391, 16145223273,76580830416,363243440911, 1722961426119,8172464117705,38764179352078, 183868863324799,872139110880993] |