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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 20 |
| 3 | 89 |
| 4 | 332 |
| 5 | 1952 |
| 6 | 10449 |
| 7 | 51825 |
| 8 | 271385 |
| 9 | 1423312 |
| 10 | 7377473 |
| 11 | 38384768 |
| 12 | 199921136 |
| 13 | 1040944841 |
| 14 | 5418020729 |
| 15 | 28200226049 |
| 16 | 146829523292 |
| 17 | 764363230209 |
| 18 | 3978793059292 |
| 19 | 20713653589248 |
| 20 | 107832120979057 |
| 21 | 561339614901057 |
[1,20,89,332,1952,10449,51825,271385,1423312, 7377473,38384768,199921136,1040944841,5418020729, 28200226049,146829523292,764363230209, 3978793059292,20713653589248,107832120979057, 561339614901057] |