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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 20 |
| 3 | 108 |
| 4 | 725 |
| 5 | 4480 |
| 6 | 28561 |
| 7 | 179928 |
| 8 | 1138660 |
| 9 | 7193450 |
| 10 | 45474461 |
| 11 | 287400960 |
| 12 | 1816564229 |
| 13 | 11481464878 |
| 14 | 72568802500 |
| 15 | 458669938608 |
| 16 | 2899021855801 |
| 17 | 18323243845760 |
| 18 | 115811947027949 |
| 19 | 731988596166300 |
| 20 | 4626528972901940 |
| 21 | 29241944603930518 |
| 22 | 184823511249946969 |
[1,2,20,108,725,4480,28561,179928,1138660,7193450, 45474461,287400960,1816564229,11481464878, 72568802500,458669938608,2899021855801, 18323243845760,115811947027949,731988596166300, 4626528972901940,29241944603930518, 184823511249946969] |