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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 4 |
| 3 | 11 |
| 4 | 40 |
| 5 | 177 |
| 6 | 934 |
| 7 | 5665 |
| 8 | 39064 |
| 9 | 301209 |
| 10 | 2572314 |
| 11 | 24156365 |
| 12 | 247234332 |
| 13 | 2751134557 |
| 14 | 33003190406 |
| 15 | 426920246945 |
| 16 | 5905698391952 |
| 17 | 87530592395793 |
| 18 | 1378247307547506 |
| 19 | 23127717388170197 |
| 20 | 409930747848171812 |
[1,2,4,11,40,177,934,5665,39064,301209,2572314, 24156365,247234332,2751134557,33003190406, 426920246945,5905698391952,87530592395793, 1378247307547506,23127717388170197, 409930747848171812] |