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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 0 |
| 3 | 1 |
| 4 | 4 |
| 5 | 10 |
| 6 | 25 |
| 7 | 45 |
| 8 | 120 |
| 9 | 399 |
| 10 | 1108 |
| 11 | 2923 |
| 12 | 7991 |
| 13 | 21953 |
| 14 | 61747 |
| 15 | 176646 |
| 16 | 499952 |
| 17 | 1409762 |
| 18 | 3999661 |
| 19 | 11391786 |
| 20 | 32574598 |
| 21 | 93459471 |
| 22 | 268336007 |
| 23 | 771070140 |
| 24 | 2219952037 |
| 25 | 6403510478 |
| 26 | 18502345737 |
| 27 | 53538515559 |
| 28 | 155090741041 |
| 29 | 449731074131 |
[1,0,1,4,10,25,45,120,399,1108,2923,7991,21953, 61747,176646,499952,1409762,3999661,11391786, 32574598,93459471,268336007,771070140,2219952037, 6403510478,18502345737,53538515559,155090741041, 449731074131] |