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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 9 |
| 4 | 50 |
| 5 | 311 |
| 6 | 2072 |
| 7 | 14460 |
| 8 | 104346 |
| 9 | 772255 |
| 10 | 5829538 |
| 11 | 44710705 |
| 12 | 347424376 |
| 13 | 2729299748 |
| 14 | 21640457360 |
| 15 | 172957598120 |
| 16 | 1391926695402 |
| 17 | 11270059892943 |
| 18 | 91740990170150 |
| 19 | 750364940281275 |
| 20 | 6163650579487170 |
| 21 | 50824871829196575 |
[1,1,2,9,50,311,2072,14460,104346,772255,5829538, 44710705,347424376,2729299748,21640457360, 172957598120,1391926695402,11270059892943, 91740990170150,750364940281275,6163650579487170, 50824871829196575] |