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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 18 |
| 3 | 130 |
| 4 | 902 |
| 5 | 6243 |
| 6 | 43375 |
| 7 | 300901 |
| 8 | 2088188 |
| 9 | 14490885 |
| 10 | 100561673 |
| 11 | 697859666 |
| 12 | 4842887731 |
| 13 | 33607835172 |
| 14 | 233225868721 |
| 15 | 1618500688831 |
| 16 | 11231792221332 |
| 17 | 77944456338104 |
| 18 | 540905507962400 |
| 19 | 3753682843565441 |
| 20 | 26049161421235915 |
[1,18,130,902,6243,43375,300901,2088188,14490885, 100561673,697859666,4842887731,33607835172, 233225868721,1618500688831,11231792221332, 77944456338104,540905507962400,3753682843565441, 26049161421235915] |