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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 2 |
| 3 | 2 |
| 4 | 12 |
| 5 | 30 |
| 6 | 130 |
| 7 | 462 |
| 8 | 1946 |
| 9 | 7980 |
| 10 | 34776 |
| 11 | 153120 |
| 12 | 694056 |
| 13 | 3194334 |
| 14 | 14971242 |
| 15 | 71133062 |
| 16 | 342500730 |
| 17 | 1667918824 |
| 18 | 8208038124 |
| 19 | 40772105244 |
| 20 | 204270936480 |
| 21 | 1031413134960 |
| 22 | 5245260798960 |
| 23 | 26850869456400 |
| 24 | 138289429433200 |
| 25 | 716247599547360 |
| 26 | 3729128330979200 |
| 27 | 19510354349803200 |
| 28 | 102540704879774160 |
[1,0,2,2,12,30,130,462,1946,7980,34776,153120, 694056,3194334,14971242,71133062,342500730, 1667918824,8208038124,40772105244,204270936480, 1031413134960,5245260798960,26850869456400, 138289429433200,716247599547360,3729128330979200, 19510354349803200,102540704879774160] |