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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 252 |
| 4 | 6822 |
| 5 | 108348 |
| 6 | 1144464 |
| 7 | 8559378 |
| 8 | 49511370 |
| 9 | 225803628 |
| 10 | 868915644 |
| 11 | 2866094766 |
| 12 | 8402366160 |
| 13 | 22207133946 |
| 14 | 53934812124 |
| 15 | 121777854570 |
| 16 | 258248878044 |
| 17 | 519141258054 |
| 18 | 994719606876 |
| 19 | 1830153826026 |
| 20 | 3242675095548 |
| 21 | 5566018125510 |
[0,0,252,6822,108348,1144464,8559378,49511370, 225803628,868915644,2866094766,8402366160, 22207133946,53934812124,121777854570,258248878044, 519141258054,994719606876,1830153826026, 3242675095548,5566018125510] |