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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 2 |
| 3 | 9 |
| 4 | 37 |
| 5 | 153 |
| 6 | 643 |
| 7 | 2745 |
| 8 | 11881 |
| 9 | 52038 |
| 10 | 230268 |
| 11 | 1028007 |
| 12 | 4625013 |
| 13 | 20949444 |
| 14 | 95462022 |
| 15 | 437318631 |
| 16 | 2012933893 |
| 17 | 9304997544 |
| 18 | 43179620542 |
| 19 | 201076887771 |
| 20 | 939358727203 |
| 21 | 4401177906249 |
| 22 | 20676208303727 |
| 23 | 97374640613139 |
[0,0,2,9,37,153,643,2745,11881,52038,230268, 1028007,4625013,20949444,95462022,437318631, 2012933893,9304997544,43179620542,201076887771, 939358727203,4401177906249,20676208303727, 97374640613139] |