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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 21 |
| 4 | 146 |
| 5 | 1210 |
| 6 | 11894 |
| 7 | 133000 |
| 8 | 1677668 |
| 9 | 23439684 |
| 10 | 359651232 |
| 11 | 6000427884 |
| 12 | 108157599120 |
| 13 | 2092493844480 |
| 14 | 43240336406136 |
| 15 | 950021322002904 |
| 16 | 22108068716440272 |
| 17 | 543048769028068944 |
| 18 | 14037848562783308160 |
| 19 | 380851191359082217488 |
| 20 | 10818262594065294568416 |
[1,1,4,21,146,1210,11894,133000,1677668,23439684, 359651232,6000427884,108157599120,2092493844480, 43240336406136,950021322002904,22108068716440272, 543048769028068944,14037848562783308160, 380851191359082217488,10818262594065294568416] |