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| n | a(n) |
|---|---|
| 1 | 4 |
| 2 | 28 |
| 3 | 115 |
| 4 | 597 |
| 5 | 2969 |
| 6 | 14502 |
| 7 | 72069 |
| 8 | 355733 |
| 9 | 1758440 |
| 10 | 8694133 |
| 11 | 42971533 |
| 12 | 212421477 |
| 13 | 1050032453 |
| 14 | 5190462389 |
| 15 | 25657338163 |
| 16 | 126828250969 |
| 17 | 626932433662 |
| 18 | 3099027752523 |
| 19 | 15318990620737 |
| 20 | 75724228662992 |
| 21 | 374317006433927 |
[4,28,115,597,2969,14502,72069,355733,1758440, 8694133,42971533,212421477,1050032453,5190462389, 25657338163,126828250969,626932433662, 3099027752523,15318990620737,75724228662992, 374317006433927] |