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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 9 |
| 3 | 73 |
| 4 | 545 |
| 5 | 3881 |
| 6 | 27761 |
| 7 | 208593 |
| 8 | 1655241 |
| 9 | 13490897 |
| 10 | 110135641 |
| 11 | 895031361 |
| 12 | 7279880713 |
| 13 | 59647817713 |
| 14 | 493774294393 |
| 15 | 4125976137817 |
| 16 | 34688652854097 |
| 17 | 292496479087385 |
| 18 | 2469649871976929 |
| 19 | 20883345481893257 |
| 20 | 177031405058676369 |
| 21 | 1505681846157691769 |
[1,1,9,73,545,3881,27761,208593,1655241,13490897, 110135641,895031361,7279880713,59647817713, 493774294393,4125976137817,34688652854097, 292496479087385,2469649871976929, 20883345481893257,177031405058676369, 1505681846157691769] |