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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 0 |
| 3 | 1 |
| 4 | 6 |
| 5 | 25 |
| 6 | 90 |
| 7 | 301 |
| 8 | 967 |
| 9 | 3061 |
| 10 | 10080 |
| 11 | 40381 |
| 12 | 245553 |
| 13 | 2161238 |
| 14 | 21701381 |
| 15 | 219007491 |
| 16 | 2149071359 |
| 17 | 20442363031 |
| 18 | 189226358659 |
| 19 | 1712836890912 |
| 20 | 15232581945180 |
| 21 | 133717667932475 |
| 22 | 1164901223314180 |
| 23 | 10143255631462661 |
| 24 | 89207257764369032 |
| 25 | 804712211338739040 |
[0,0,0,1,6,25,90,301,967,3061,10080,40381,245553, 2161238,21701381,219007491,2149071359,20442363031, 189226358659,1712836890912,15232581945180, 133717667932475,1164901223314180, 10143255631462661,89207257764369032, 804712211338739040] |