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| n | a(n) |
|---|---|
| 1 | 520 |
| 2 | 2920 |
| 3 | 13906 |
| 4 | 60508 |
| 5 | 249512 |
| 6 | 995624 |
| 7 | 3894542 |
| 8 | 15061244 |
| 9 | 57914756 |
| 10 | 222291368 |
| 11 | 853854042 |
| 12 | 3287692860 |
| 13 | 12701872800 |
| 14 | 49262782920 |
| 15 | 191821043814 |
| 16 | 749801489244 |
| 17 | 2941369935292 |
| 18 | 11575782602248 |
| 19 | 45685412767666 |
| 20 | 180742482085084 |
[520,2920,13906,60508,249512,995624,3894542, 15061244,57914756,222291368,853854042,3287692860, 12701872800,49262782920,191821043814,749801489244, 2941369935292,11575782602248,45685412767666, 180742482085084] |