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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 5 |
| 4 | 15 |
| 5 | 52 |
| 6 | 201 |
| 7 | 857 |
| 8 | 4370 |
| 9 | 34365 |
| 10 | 478287 |
| 11 | 9095996 |
| 12 | 189526537 |
| 13 | 4036216585 |
| 14 | 87129122290 |
| 15 | 2478683501397 |
| 16 | 2450240534552191 |
| 17 | 12482183328151728692 |
| 18 | 65634092872761268943625 |
| 19 | 345370818796643845031835465 |
| 20 | 1817414952852912380501431441282 |
[1,1,2,5,15,52,201,857,4370,34365,478287,9095996, 189526537,4036216585,87129122290,2478683501397, 2450240534552191,12482183328151728692, 65634092872761268943625, 345370818796643845031835465, 1817414952852912380501431441282] |