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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 1 |
| 3 | 0 |
| 4 | 6 |
| 5 | 20 |
| 6 | 135 |
| 7 | 924 |
| 8 | 7420 |
| 9 | 66744 |
| 10 | 667485 |
| 11 | 7342280 |
| 12 | 88107426 |
| 13 | 1145396460 |
| 14 | 16035550531 |
| 15 | 240533257860 |
| 16 | 3848532125880 |
| 17 | 65425046139824 |
| 18 | 1177650830516985 |
| 19 | 22375365779822544 |
| 20 | 447507315596451070 |
| 21 | 9397653627525472260 |
| 22 | 206748379805560389951 |
| 23 | 4755212735527888968620 |
[0,0,1,0,6,20,135,924,7420,66744,667485,7342280, 88107426,1145396460,16035550531,240533257860, 3848532125880,65425046139824,1177650830516985, 22375365779822544,447507315596451070, 9397653627525472260,206748379805560389951, 4755212735527888968620] |