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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 20 |
| 2 | 210 |
| 3 | 1560 |
| 4 | 9255 |
| 5 | 46724 |
| 6 | 208510 |
| 7 | 843320 |
| 8 | 3145855 |
| 9 | 10963160 |
| 10 | 36042250 |
| 11 | 112633760 |
| 12 | 336622160 |
| 13 | 966897820 |
| 14 | 2680139300 |
| 15 | 7193849624 |
| 16 | 18752326235 |
| 17 | 47590579080 |
| 18 | 117840608100 |
| 19 | 285228791880 |
| 20 | 675978772326 |
| 21 | 1570897356960 |
| 22 | 3584273539170 |
| 23 | 8038904002760 |
| 24 | 17741382028085 |
| 25 | 38563932406500 |
[1,20,210,1560,9255,46724,208510,843320,3145855, 10963160,36042250,112633760,336622160,966897820, 2680139300,7193849624,18752326235,47590579080, 117840608100,285228791880,675978772326, 1570897356960,3584273539170,8038904002760, 17741382028085,38563932406500] |