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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 4 |
| 3 | 10 |
| 4 | 21 |
| 5 | 89 |
| 6 | 248 |
| 7 | 1652 |
| 8 | 5760 |
| 9 | 59789 |
| 10 | 268529 |
| 11 | 4367552 |
| 12 | 24922412 |
| 13 | 641484896 |
| 14 | 4607113999 |
| 15 | 188770443286 |
| 16 | 1702258930069 |
| 17 | 111575238563044 |
| 18 | 1256539208451845 |
| 19 | 132483845142611245 |
| 20 | 1854392449274745630 |
| 21 | 316017552098202250347 |
[1,2,4,10,21,89,248,1652,5760,59789,268529, 4367552,24922412,641484896,4607113999, 188770443286,1702258930069,111575238563044, 1256539208451845,132483845142611245, 1854392449274745630,316017552098202250347] |