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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 22 |
| 4 | 148 |
| 5 | 1132 |
| 6 | 9484 |
| 7 | 85066 |
| 8 | 804556 |
| 9 | 7939738 |
| 10 | 81128800 |
| 11 | 853424464 |
| 12 | 9201391456 |
| 13 | 101327618056 |
| 14 | 1136518296892 |
| 15 | 12954283592578 |
| 16 | 149770265417692 |
| 17 | 1753615603901818 |
| 18 | 20766700361401336 |
| 19 | 248449277456597908 |
| 20 | 3000039734827403608 |
| 21 | 36532024054221028576 |
| 22 | 448294209318801516064 |
[1,1,4,22,148,1132,9484,85066,804556,7939738, 81128800,853424464,9201391456,101327618056, 1136518296892,12954283592578,149770265417692, 1753615603901818,20766700361401336, 248449277456597908,3000039734827403608, 36532024054221028576,448294209318801516064] |