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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 20 |
| 2 | 165 |
| 3 | 880 |
| 4 | 3575 |
| 5 | 12012 |
| 6 | 35035 |
| 7 | 91520 |
| 8 | 218790 |
| 9 | 486200 |
| 10 | 1016158 |
| 11 | 2015520 |
| 12 | 3821090 |
| 13 | 6963880 |
| 14 | 12257850 |
| 15 | 20920064 |
| 16 | 34730575 |
| 17 | 56241900 |
| 18 | 89049675 |
| 19 | 138138000 |
| 20 | 210315105 |
| 21 | 314757300 |
| 22 | 463681725 |
| 23 | 673171200 |
| 24 | 964177500 |
| 25 | 1363732656 |
| 26 | 1906401420 |
| 27 | 2636011840 |
| 28 | 3607704980 |
[1,20,165,880,3575,12012,35035,91520,218790, 486200,1016158,2015520,3821090,6963880,12257850, 20920064,34730575,56241900,89049675,138138000, 210315105,314757300,463681725,673171200,964177500, 1363732656,1906401420,2636011840,3607704980] |