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| n | a(n) |
|---|---|
| 1 | -1 |
| 2 | 2 |
| 3 | 37 |
| 4 | 324 |
| 5 | 2403 |
| 6 | 16582 |
| 7 | 109961 |
| 8 | 711176 |
| 9 | 4521607 |
| 10 | 28394442 |
| 11 | 176648877 |
| 12 | 1090974156 |
| 13 | 6698429931 |
| 14 | 40930511502 |
| 15 | 249105886737 |
| 16 | 1510954029072 |
| 17 | 9138180665871 |
| 18 | 55128765109906 |
| 19 | 331851698655797 |
| 20 | 1993747216968788 |
[-1,2,37,324,2403,16582,109961,711176,4521607, 28394442,176648877,1090974156,6698429931, 40930511502,249105886737,1510954029072, 9138180665871,55128765109906,331851698655797, 1993747216968788] |