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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 34 |
| 3 | 352 |
| 4 | 3946 |
| 5 | 46744 |
| 6 | 573616 |
| 7 | 7217536 |
| 8 | 92527738 |
| 9 | 1203467464 |
| 10 | 15834369244 |
| 11 | 210304283776 |
| 12 | 2815055712496 |
| 13 | 37930536447808 |
| 14 | 513972867056704 |
| 15 | 6998587355233792 |
| 16 | 95704396144575898 |
| 17 | 1313665229153722408 |
| 18 | 18091969874675059204 |
| 19 | 249908773119244105792 |
[1,4,34,352,3946,46744,573616,7217536,92527738, 1203467464,15834369244,210304283776,2815055712496, 37930536447808,513972867056704,6998587355233792, 95704396144575898,1313665229153722408, 18091969874675059204,249908773119244105792] |