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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 20 |
| 2 | 209 |
| 3 | 1519 |
| 4 | 8624 |
| 5 | 40734 |
| 6 | 166495 |
| 7 | 604902 |
| 8 | 1991637 |
| 9 | 6029727 |
| 10 | 16976806 |
| 11 | 44853151 |
| 12 | 112016669 |
| 13 | 266039599 |
| 14 | 603919164 |
| 15 | 1315952428 |
| 16 | 2762629983 |
| 17 | 5605337934 |
| 18 | 11022366544 |
| 19 | 21056764914 |
| 20 | 39163212165 |
| 21 | 71048746505 |
[1,20,209,1519,8624,40734,166495,604902,1991637, 6029727,16976806,44853151,112016669,266039599, 603919164,1315952428,2762629983,5605337934, 11022366544,21056764914,39163212165,71048746505] |