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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 4 |
| 3 | 9 |
| 4 | 40 |
| 5 | 120 |
| 6 | 390 |
| 7 | 1176 |
| 8 | 3536 |
| 9 | 10395 |
| 10 | 30260 |
| 11 | 87120 |
| 12 | 248844 |
| 13 | 705744 |
| 14 | 1989820 |
| 15 | 5581485 |
| 16 | 15586720 |
| 17 | 43356936 |
| 18 | 120187026 |
| 19 | 332134440 |
| 20 | 915304520 |
| 21 | 2516113215 |
| 22 | 6900949484 |
| 23 | 18888143904 |
| 24 | 51599794200 |
| 25 | 140718765600 |
| 26 | 383142771700 |
| 27 | 1041660829521 |
| 28 | 2828107288216 |
| 29 | 7668512468760 |
| 30 | 20768716848030 |
| 31 | 56185646831160 |
| 32 | 151840963183424 |
| 33 | 409947452576739 |
| 34 | 1105779284582180 |
| 35 | 2980113861417840 |
[0,4,9,40,120,390,1176,3536,10395,30260,87120, 248844,705744,1989820,5581485,15586720,43356936, 120187026,332134440,915304520,2516113215, 6900949484,18888143904,51599794200,140718765600, 383142771700,1041660829521,2828107288216, 7668512468760,20768716848030,56185646831160, 151840963183424,409947452576739,1105779284582180, 2980113861417840] |