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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 3 |
| 2 | 18 |
| 3 | 136 |
| 4 | 1152 |
| 5 | 10458 |
| 6 | 99472 |
| 7 | 978453 |
| 8 | 9871686 |
| 9 | 101590654 |
| 10 | 1062271704 |
| 11 | 11253818628 |
| 12 | 120535386692 |
| 13 | 1303045817184 |
| 14 | 14199323523912 |
| 15 | 155805565801803 |
| 16 | 1720024043803542 |
| 17 | 19090440094335912 |
| 18 | 212897898182054224 |
| 19 | 2384431948345110510 |
| 20 | 26808516659219953680 |
[1,3,18,136,1152,10458,99472,978453,9871686, 101590654,1062271704,11253818628,120535386692, 1303045817184,14199323523912,155805565801803, 1720024043803542,19090440094335912, 212897898182054224,2384431948345110510, 26808516659219953680] |