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| n | a(n) |
|---|---|
| 1 | 21 |
| 2 | 237 |
| 3 | 311 |
| 4 | 1666 |
| 5 | 8887 |
| 6 | 32359 |
| 7 | 135880 |
| 8 | 617692 |
| 9 | 2534229 |
| 10 | 10679366 |
| 11 | 46580215 |
| 12 | 196401620 |
| 13 | 830912246 |
| 14 | 3573030794 |
| 15 | 15182231394 |
| 16 | 64434941953 |
| 17 | 275517063290 |
| 18 | 1173301166480 |
| 19 | 4989227156149 |
| 20 | 21285269812669 |
| 21 | 90693224894008 |
[21,237,311,1666,8887,32359,135880,617692,2534229, 10679366,46580215,196401620,830912246,3573030794, 15182231394,64434941953,275517063290, 1173301166480,4989227156149,21285269812669, 90693224894008] |