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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 0 |
| 3 | 6 |
| 4 | 12 |
| 5 | 20 |
| 6 | 1110 |
| 7 | 10122 |
| 8 | 58856 |
| 9 | 1239912 |
| 10 | 23773770 |
| 11 | 303367790 |
| 12 | 5442263772 |
| 13 | 135931189836 |
| 14 | 2868815413646 |
| 15 | 61708462976370 |
| 16 | 1696559552295120 |
| 17 | 48121891688969552 |
| 18 | 1323641220801211026 |
| 19 | 40678367069424137814 |
| 20 | 1372011621943725532100 |
[1,0,0,6,12,20,1110,10122,58856,1239912,23773770, 303367790,5442263772,135931189836,2868815413646, 61708462976370,1696559552295120,48121891688969552, 1323641220801211026,40678367069424137814, 1372011621943725532100] |