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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 18 |
| 3 | 86 |
| 4 | 428 |
| 5 | 2192 |
| 6 | 11468 |
| 7 | 60986 |
| 8 | 328532 |
| 9 | 1788368 |
| 10 | 9819128 |
| 11 | 54302712 |
| 12 | 302157424 |
| 13 | 1690193728 |
| 14 | 9497996152 |
| 15 | 53588976802 |
| 16 | 303434431108 |
| 17 | 1723578967056 |
| 18 | 9818195961512 |
| 19 | 56071829010968 |
| 20 | 320970950634288 |
| 21 | 1841213871449152 |
| 22 | 10582333064327824 |
| 23 | 60929582362628968 |
| 24 | 351385363433883472 |
[1,4,18,86,428,2192,11468,60986,328532,1788368, 9819128,54302712,302157424,1690193728,9497996152, 53588976802,303434431108,1723578967056, 9818195961512,56071829010968,320970950634288, 1841213871449152,10582333064327824, 60929582362628968,351385363433883472] |