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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 5 |
| 3 | 15 |
| 4 | 52 |
| 5 | 205 |
| 6 | 921 |
| 7 | 4766 |
| 8 | 28685 |
| 9 | 201159 |
| 10 | 1630840 |
| 11 | 15071725 |
| 12 | 156331161 |
| 13 | 1794763970 |
| 14 | 22548418541 |
| 15 | 307236496071 |
| 16 | 4507944378004 |
| 17 | 70813851019717 |
| 18 | 1185225078743601 |
| 19 | 21049903662123422 |
| 20 | 395303080572770549 |
| 21 | 7825181077750155999 |
| 22 | 162835332607069248760 |
[1,2,5,15,52,205,921,4766,28685,201159,1630840, 15071725,156331161,1794763970,22548418541, 307236496071,4507944378004,70813851019717, 1185225078743601,21049903662123422, 395303080572770549,7825181077750155999, 162835332607069248760] |