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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 1 |
| 4 | 2 |
| 5 | 9 |
| 6 | 29 |
| 7 | 79 |
| 8 | 220 |
| 9 | 673 |
| 10 | 2106 |
| 11 | 6480 |
| 12 | 19803 |
| 13 | 61085 |
| 14 | 190155 |
| 15 | 593635 |
| 16 | 1854310 |
| 17 | 5802490 |
| 18 | 18203576 |
| 19 | 57227627 |
| 20 | 180170568 |
| 21 | 567940927 |
| 22 | 1792532647 |
| 23 | 5664324570 |
| 24 | 17917857888 |
| 25 | 56732156348 |
| 26 | 179781808709 |
| 27 | 570178314799 |
| 28 | 1809666098574 |
[1,1,1,2,9,29,79,220,673,2106,6480,19803,61085, 190155,593635,1854310,5802490,18203576,57227627, 180170568,567940927,1792532647,5664324570, 17917857888,56732156348,179781808709,570178314799, 1809666098574] |