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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 26 |
| 3 | 202 |
| 4 | 1729 |
| 5 | 15730 |
| 6 | 149249 |
| 7 | 1460300 |
| 8 | 14627340 |
| 9 | 149254996 |
| 10 | 1545959720 |
| 11 | 16212144520 |
| 12 | 171789072036 |
| 13 | 1836515799464 |
| 14 | 19783708310984 |
| 15 | 214539449634588 |
| 16 | 2340148164406642 |
| 17 | 25658221358522584 |
| 18 | 282627226176802000 |
| 19 | 3126081536554547488 |
| 20 | 34706443838025828198 |
[1,4,26,202,1729,15730,149249,1460300,14627340, 149254996,1545959720,16212144520,171789072036, 1836515799464,19783708310984,214539449634588, 2340148164406642,25658221358522584, 282627226176802000,3126081536554547488, 34706443838025828198] |