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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 28 |
| 3 | 109 |
| 4 | 380 |
| 5 | 2450 |
| 6 | 12075 |
| 7 | 55471 |
| 8 | 286079 |
| 9 | 1429824 |
| 10 | 6989477 |
| 11 | 34856362 |
| 12 | 173451524 |
| 13 | 858586095 |
| 14 | 4263159553 |
| 15 | 21172762001 |
| 16 | 105041615196 |
| 17 | 521348098233 |
| 18 | 2587930504660 |
| 19 | 12843811121650 |
| 20 | 63746482751185 |
| 21 | 316398514788731 |
[1,28,109,380,2450,12075,55471,286079,1429824, 6989477,34856362,173451524,858586095,4263159553, 21172762001,105041615196,521348098233, 2587930504660,12843811121650,63746482751185, 316398514788731] |