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| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 1 |
| 3 | 1 |
| 4 | 5 |
| 5 | 22 |
| 6 | 99 |
| 7 | 450 |
| 8 | 2067 |
| 9 | 9586 |
| 10 | 44852 |
| 11 | 211570 |
| 12 | 1005427 |
| 13 | 4810460 |
| 14 | 23157904 |
| 15 | 112110906 |
| 16 | 545524287 |
| 17 | 2666864340 |
| 18 | 13092764136 |
| 19 | 64527778938 |
| 20 | 319157531592 |
| 21 | 1583724160896 |
| 22 | 7882364163954 |
| 23 | 39339994155288 |
| 24 | 196843821874407 |
| 25 | 987272738842392 |
[2,1,1,5,22,99,450,2067,9586,44852,211570,1005427, 4810460,23157904,112110906,545524287,2666864340, 13092764136,64527778938,319157531592, 1583724160896,7882364163954,39339994155288, 196843821874407,987272738842392] |