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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 15 |
| 3 | 54 |
| 4 | 192 |
| 5 | 682 |
| 6 | 2431 |
| 7 | 8710 |
| 8 | 31382 |
| 9 | 113696 |
| 10 | 414086 |
| 11 | 1515516 |
| 12 | 5571750 |
| 13 | 20569590 |
| 14 | 76228095 |
| 15 | 283481670 |
| 16 | 1057628550 |
| 17 | 3957577800 |
| 18 | 14849601090 |
| 19 | 55859886420 |
| 20 | 210622646520 |
| 21 | 795898303668 |
| 22 | 3013646759910 |
| 23 | 11432740177564 |
| 24 | 43448822603452 |
| 25 | 165396657221152 |
[1,4,15,54,192,682,2431,8710,31382,113696,414086, 1515516,5571750,20569590,76228095,283481670, 1057628550,3957577800,14849601090,55859886420, 210622646520,795898303668,3013646759910, 11432740177564,43448822603452,165396657221152] |