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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 21 |
| 2 | 99 |
| 3 | 475 |
| 4 | 2293 |
| 5 | 11111 |
| 6 | 53973 |
| 7 | 262649 |
| 8 | 1279855 |
| 9 | 6243155 |
| 10 | 30479985 |
| 11 | 148910385 |
| 12 | 727918557 |
| 13 | 3559976043 |
| 14 | 17417455619 |
| 15 | 85244931269 |
| 16 | 417326666085 |
| 17 | 2043565752795 |
| 18 | 10008988327829 |
| 19 | 49030629716903 |
| 20 | 240219997723397 |
[1,21,99,475,2293,11111,53973,262649,1279855, 6243155,30479985,148910385,727918557,3559976043, 17417455619,85244931269,417326666085, 2043565752795,10008988327829,49030629716903, 240219997723397] |