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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 23 |
| 5 | 110 |
| 6 | 630 |
| 7 | 4200 |
| 8 | 31990 |
| 9 | 274051 |
| 10 | 2608220 |
| 11 | 27304530 |
| 12 | 311820630 |
| 13 | 3857738170 |
| 14 | 51397726380 |
| 15 | 733698365400 |
| 16 | 11171708347799 |
| 17 | 180738402744866 |
| 18 | 3096027531044102 |
| 19 | 55980949167688884 |
| 20 | 1065496642477438890 |
| 21 | 21293801805033731190 |
| 22 | 445818117237227995260 |
[1,1,2,6,23,110,630,4200,31990,274051,2608220, 27304530,311820630,3857738170,51397726380, 733698365400,11171708347799,180738402744866, 3096027531044102,55980949167688884, 1065496642477438890,21293801805033731190, 445818117237227995260] |