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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 5 |
| 3 | 18 |
| 4 | 89 |
| 5 | 546 |
| 6 | 3893 |
| 7 | 31210 |
| 8 | 276393 |
| 9 | 2674346 |
| 10 | 28053749 |
| 11 | 317122018 |
| 12 | 3843832473 |
| 13 | 49745582994 |
| 14 | 684808185109 |
| 15 | 9994279232186 |
| 16 | 154164863607273 |
| 17 | 2506527296803674 |
| 18 | 42846740489105301 |
| 19 | 768278266512841330 |
[1,2,5,18,89,546,3893,31210,276393,2674346, 28053749,317122018,3843832473,49745582994, 684808185109,9994279232186,154164863607273, 2506527296803674,42846740489105301, 768278266512841330] |