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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 2 |
| 3 | 15 |
| 4 | 52 |
| 5 | 269 |
| 6 | 1110 |
| 7 | 5179 |
| 8 | 22568 |
| 9 | 102105 |
| 10 | 452458 |
| 11 | 2028071 |
| 12 | 9033180 |
| 13 | 40375141 |
| 14 | 180115262 |
| 15 | 804357075 |
| 16 | 3589982032 |
| 17 | 16027891889 |
| 18 | 71545586130 |
| 19 | 319397983039 |
| 20 | 1425797413508 |
| 21 | 6364972640445 |
| 22 | 28413716829478 |
[0,1,2,15,52,269,1110,5179,22568,102105,452458, 2028071,9033180,40375141,180115262,804357075, 3589982032,16027891889,71545586130,319397983039, 1425797413508,6364972640445,28413716829478] |