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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 4 |
| 3 | 34 |
| 4 | 216 |
| 5 | 1525 |
| 6 | 10336 |
| 7 | 71149 |
| 8 | 486864 |
| 9 | 3339106 |
| 10 | 22881100 |
| 11 | 156843721 |
| 12 | 1074985344 |
| 13 | 7368157369 |
| 14 | 50501844796 |
| 15 | 346145466850 |
| 16 | 2372514562656 |
| 17 | 16261461342589 |
| 18 | 111457702083424 |
| 19 | 763942486626661 |
| 20 | 5236139616899400 |
[0,1,4,34,216,1525,10336,71149,486864,3339106, 22881100,156843721,1074985344,7368157369, 50501844796,346145466850,2372514562656, 16261461342589,111457702083424,763942486626661, 5236139616899400] |