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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 6 |
| 2 | 25 |
| 3 | 90 |
| 4 | 300 |
| 5 | 954 |
| 6 | 2939 |
| 7 | 8850 |
| 8 | 26195 |
| 9 | 76500 |
| 10 | 221016 |
| 11 | 632916 |
| 12 | 1799125 |
| 13 | 5082270 |
| 14 | 14279725 |
| 15 | 39935214 |
| 16 | 111228804 |
| 17 | 308681550 |
| 18 | 853904015 |
| 19 | 2355364650 |
| 20 | 6480104231 |
| 21 | 17786356776 |
| 22 | 48715278000 |
| 23 | 133167004200 |
| 24 | 363372003625 |
| 25 | 989900286774 |
[1,6,25,90,300,954,2939,8850,26195,76500,221016, 632916,1799125,5082270,14279725,39935214, 111228804,308681550,853904015,2355364650, 6480104231,17786356776,48715278000,133167004200, 363372003625,989900286774] |