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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 19 |
| 3 | 72 |
| 4 | 341 |
| 5 | 1292 |
| 6 | 6119 |
| 7 | 23184 |
| 8 | 109801 |
| 9 | 416020 |
| 10 | 1970299 |
| 11 | 7465176 |
| 12 | 35355581 |
| 13 | 133957148 |
| 14 | 634430159 |
| 15 | 2403763488 |
| 16 | 11384387281 |
| 17 | 43133785636 |
| 18 | 204284540899 |
| 19 | 774004377960 |
| 20 | 3665737348901 |
| 21 | 13888945017644 |
| 22 | 65778987739319 |
[1,4,19,72,341,1292,6119,23184,109801,416020, 1970299,7465176,35355581,133957148,634430159, 2403763488,11384387281,43133785636,204284540899, 774004377960,3665737348901,13888945017644, 65778987739319] |