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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 0 |
| 5 | 1 |
| 6 | 2 |
| 7 | 4 |
| 8 | 16 |
| 9 | 60 |
| 10 | 186 |
| 11 | 433 |
| 12 | 2215 |
| 13 | 11788 |
| 14 | 76539 |
| 15 | 414240 |
| 16 | 2202215 |
| 17 | 9655287 |
| 18 | 69748712 |
| 19 | 444195809 |
| 20 | 3703859949 |
| 21 | 26688275292 |
| 22 | 201673532931 |
| 23 | 1265944917365 |
| 24 | 11801735916539 |
| 25 | 92511897525830 |
| 26 | 753795624276096 |
| 27 | 5237677221537738 |
| 28 | 41074291450736424 |
| 29 | 280906738160126067 |
[0,0,0,0,1,2,4,16,60,186,433,2215,11788,76539, 414240,2202215,9655287,69748712,444195809, 3703859949,26688275292,201673532931,1265944917365, 11801735916539,92511897525830,753795624276096, 5237677221537738,41074291450736424, 280906738160126067] |