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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 7 |
| 2 | 56 |
| 3 | 455 |
| 4 | 3710 |
| 5 | 30282 |
| 6 | 247254 |
| 7 | 2019087 |
| 8 | 16488710 |
| 9 | 134656130 |
| 10 | 1099686056 |
| 11 | 8980749862 |
| 12 | 73342721956 |
| 13 | 598965319960 |
| 14 | 4891549246290 |
| 15 | 39947649057855 |
| 16 | 326239122661830 |
| 17 | 2664286127154330 |
| 18 | 21758336553841440 |
| 19 | 177693081299126610 |
[1,7,56,455,3710,30282,247254,2019087,16488710, 134656130,1099686056,8980749862,73342721956, 598965319960,4891549246290,39947649057855, 326239122661830,2664286127154330, 21758336553841440,177693081299126610] |