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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 15 |
| 3 | 128 |
| 4 | 945 |
| 5 | 6655 |
| 6 | 46080 |
| 7 | 317057 |
| 8 | 2176335 |
| 9 | 14925184 |
| 10 | 102320625 |
| 11 | 701373311 |
| 12 | 4807434240 |
| 13 | 32951037313 |
| 14 | 225850798095 |
| 15 | 1548007091840 |
| 16 | 10610205501105 |
| 17 | 72723448842367 |
| 18 | 498453982018560 |
| 19 | 3416454544730369 |
| 20 | 23416728143799375 |
[0,1,15,128,945,6655,46080,317057,2176335, 14925184,102320625,701373311,4807434240, 32951037313,225850798095,1548007091840, 10610205501105,72723448842367,498453982018560, 3416454544730369,23416728143799375] |