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| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 12 |
| 3 | 76 |
| 4 | 492 |
| 5 | 3212 |
| 6 | 21036 |
| 7 | 137932 |
| 8 | 904812 |
| 9 | 5936396 |
| 10 | 38950572 |
| 11 | 255572812 |
| 12 | 1676946156 |
| 13 | 11003350412 |
| 14 | 72199015212 |
| 15 | 473737530316 |
| 16 | 3108453529452 |
| 17 | 20396281280012 |
| 18 | 133831275048876 |
| 19 | 878140974959692 |
| 20 | 5761968373855212 |
[2,12,76,492,3212,21036,137932,904812,5936396, 38950572,255572812,1676946156,11003350412, 72199015212,473737530316,3108453529452, 20396281280012,133831275048876,878140974959692, 5761968373855212] |