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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 272 |
| 3 | 9963 |
| 4 | 131584 |
| 5 | 978125 |
| 6 | 5042736 |
| 7 | 20185207 |
| 8 | 67125248 |
| 9 | 193739769 |
| 10 | 500050000 |
| 11 | 1179054371 |
| 12 | 2580014592 |
| 13 | 5302435333 |
| 14 | 10330792304 |
| 15 | 19222059375 |
| 16 | 34360262656 |
| 17 | 59294648177 |
| 18 | 99180589968 |
| 19 | 161345086939 |
| 20 | 256001600000 |
[0,1,272,9963,131584,978125,5042736,20185207, 67125248,193739769,500050000,1179054371, 2580014592,5302435333,10330792304,19222059375, 34360262656,59294648177,99180589968,161345086939, 256001600000] |