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| n | a(n) |
|---|---|
| 1 | 4 |
| 2 | 25 |
| 3 | 136 |
| 4 | 753 |
| 5 | 4160 |
| 6 | 22989 |
| 7 | 127037 |
| 8 | 702009 |
| 9 | 3879313 |
| 10 | 21437148 |
| 11 | 118462034 |
| 12 | 654623158 |
| 13 | 3617458391 |
| 14 | 19990134860 |
| 15 | 110465815644 |
| 16 | 610435923087 |
| 17 | 3373279000591 |
| 18 | 18640795512630 |
| 19 | 103009344107857 |
| 20 | 569231338133692 |
[4,25,136,753,4160,22989,127037,702009,3879313, 21437148,118462034,654623158,3617458391, 19990134860,110465815644,610435923087, 3373279000591,18640795512630,103009344107857, 569231338133692] |