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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 24 |
| 3 | 153 |
| 4 | 998 |
| 5 | 6586 |
| 6 | 43761 |
| 7 | 292060 |
| 8 | 1955130 |
| 9 | 13116793 |
| 10 | 88142646 |
| 11 | 593041755 |
| 12 | 3993997033 |
| 13 | 26919539964 |
| 14 | 181551848888 |
| 15 | 1225061008029 |
| 16 | 8269904756032 |
| 17 | 55846867568653 |
| 18 | 377249292917109 |
| 19 | 2548999356721459 |
| 20 | 17226879374556972 |
| 21 | 116446327805377871 |
| 22 | 787256381742222535 |
[1,4,24,153,998,6586,43761,292060,1955130, 13116793,88142646,593041755,3993997033, 26919539964,181551848888,1225061008029, 8269904756032,55846867568653,377249292917109, 2548999356721459,17226879374556972, 116446327805377871,787256381742222535] |