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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 20 |
| 2 | 210 |
| 3 | 1539 |
| 4 | 8835 |
| 5 | 42294 |
| 6 | 175559 |
| 7 | 648925 |
| 8 | 2177361 |
| 9 | 6728260 |
| 10 | 19363355 |
| 11 | 52364721 |
| 12 | 134036525 |
| 13 | 326685790 |
| 14 | 761961825 |
| 15 | 1707940096 |
| 16 | 3692525360 |
| 17 | 7724060310 |
| 18 | 15675545395 |
| 19 | 30937970105 |
| 20 | 59507001114 |
| 21 | 111753986081 |
[1,20,210,1539,8835,42294,175559,648925,2177361, 6728260,19363355,52364721,134036525,326685790, 761961825,1707940096,3692525360,7724060310, 15675545395,30937970105,59507001114,111753986081] |