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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 9 |
| 3 | 60 |
| 4 | 432 |
| 5 | 3378 |
| 6 | 27792 |
| 7 | 237122 |
| 8 | 2079132 |
| 9 | 18620709 |
| 10 | 169614960 |
| 11 | 1566540573 |
| 12 | 14635978998 |
| 13 | 138080055192 |
| 14 | 1313596636812 |
| 15 | 12587218990644 |
| 16 | 121378106852988 |
| 17 | 1176981533610012 |
| 18 | 11469587139406515 |
| 19 | 112265849283068877 |
| 20 | 1103256200355696855 |
[1,2,9,60,432,3378,27792,237122,2079132,18620709, 169614960,1566540573,14635978998,138080055192, 1313596636812,12587218990644,121378106852988, 1176981533610012,11469587139406515, 112265849283068877,1103256200355696855] |