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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 21 |
| 2 | 273 |
| 3 | 2716 |
| 4 | 22659 |
| 5 | 165984 |
| 6 | 1098615 |
| 7 | 6695559 |
| 8 | 38085117 |
| 9 | 204218630 |
| 10 | 1040291595 |
| 11 | 5064987207 |
| 12 | 23686610269 |
| 13 | 106828575357 |
| 14 | 466231753944 |
| 15 | 1974651627802 |
| 16 | 8136148603086 |
| 17 | 32681975601387 |
| 18 | 128221943065839 |
[1,21,273,2716,22659,165984,1098615,6695559, 38085117,204218630,1040291595,5064987207, 23686610269,106828575357,466231753944, 1974651627802,8136148603086,32681975601387, 128221943065839] |