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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 15 |
| 3 | 90 |
| 4 | 350 |
| 5 | 1050 |
| 6 | 2646 |
| 7 | 5880 |
| 8 | 11880 |
| 9 | 22275 |
| 10 | 39325 |
| 11 | 66066 |
| 12 | 106470 |
| 13 | 165620 |
| 14 | 249900 |
| 15 | 367200 |
| 16 | 527136 |
| 17 | 741285 |
| 18 | 1023435 |
| 19 | 1389850 |
| 20 | 1859550 |
| 21 | 2454606 |
| 22 | 3200450 |
| 23 | 4126200 |
| 24 | 5265000 |
| 25 | 6654375 |
| 26 | 8336601 |
| 27 | 10359090 |
| 28 | 12774790 |
| 29 | 15642600 |
| 30 | 19027800 |
[0,1,15,90,350,1050,2646,5880,11880,22275,39325, 66066,106470,165620,249900,367200,527136,741285, 1023435,1389850,1859550,2454606,3200450,4126200, 5265000,6654375,8336601,10359090,12774790, 15642600,19027800] |