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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 1 |
| 5 | 6 |
| 6 | 37 |
| 7 | 182 |
| 8 | 876 |
| 9 | 3920 |
| 10 | 17175 |
| 11 | 73030 |
| 12 | 306296 |
| 13 | 1266916 |
| 14 | 5198207 |
| 15 | 21180642 |
| 16 | 85909216 |
| 17 | 347179440 |
| 18 | 1399443775 |
| 19 | 5629876910 |
| 20 | 22616222616 |
| 21 | 90754709276 |
| 22 | 363889980927 |
| 23 | 1458171985402 |
| 24 | 5840531023856 |
| 25 | 23385647663560 |
| 26 | 93613189390175 |
| 27 | 374664530448390 |
[0,0,0,1,6,37,182,876,3920,17175,73030,306296, 1266916,5198207,21180642,85909216,347179440, 1399443775,5629876910,22616222616,90754709276, 363889980927,1458171985402,5840531023856, 23385647663560,93613189390175,374664530448390] |