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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 25 |
| 4 | 130 |
| 5 | 774 |
| 6 | 5009 |
| 7 | 34231 |
| 8 | 242988 |
| 9 | 1773767 |
| 10 | 13229272 |
| 11 | 100362848 |
| 12 | 772016385 |
| 13 | 6007208105 |
| 14 | 47198747457 |
| 15 | 373929821070 |
| 16 | 2983774582206 |
| 17 | 23958802697161 |
| 18 | 193448157014605 |
| 19 | 1569625544848531 |
| 20 | 12791865082236462 |
[1,2,6,25,130,774,5009,34231,242988,1773767, 13229272,100362848,772016385,6007208105, 47198747457,373929821070,2983774582206, 23958802697161,193448157014605,1569625544848531, 12791865082236462] |