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| n | a(n) |
|---|---|
| 3 | 1 |
| 4 | 4 |
| 5 | 13 |
| 6 | 28 |
| 7 | 111 |
| 8 | 502 |
| 9 | 2990 |
| 10 | 22461 |
| 11 | 175998 |
| 12 | 1776694 |
| 13 | 23271927 |
| 14 | 358397754 |
| 15 | 6862062854 |
| 16 | 158641875413 |
| 17 | 4463737522965 |
| 18 | 156583615357383 |
[1,4,13,28,111,502,2990,22461,175998,1776694, 23271927,358397754,6862062854,158641875413, 4463737522965,156583615357383] |