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| n | a(n) |
|---|---|
| 1 | 4 |
| 2 | 34 |
| 3 | 145 |
| 4 | 747 |
| 5 | 4090 |
| 6 | 21116 |
| 7 | 110551 |
| 8 | 582755 |
| 9 | 3055652 |
| 10 | 16036278 |
| 11 | 84225551 |
| 12 | 442157803 |
| 13 | 2321279598 |
| 14 | 12187515422 |
| 15 | 63986012963 |
| 16 | 335934438957 |
| 17 | 1763713210610 |
| 18 | 9259764998068 |
| 19 | 48615161059469 |
| 20 | 255237152397199 |
| 21 | 1340034403055100 |
[4,34,145,747,4090,21116,110551,582755,3055652, 16036278,84225551,442157803,2321279598, 12187515422,63986012963,335934438957, 1763713210610,9259764998068,48615161059469, 255237152397199,1340034403055100] |